diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode101.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode101.java
new file mode 100644
index 0000000..d8e9456
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode101.java
@@ -0,0 +1,35 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import cn.whaifree.leetCode.model.TreeNode;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/28 0:16
+ * @注释
+ */
+public class LeetCode101 {
+
+    public static void main(String[] args) {
+        System.out.println("hello world");
+        System.out.println(isSymmetric(TreeNode.constructTree(new Integer[]{1, 2, 2, 3, 1, 4, 3})));
+    }
+    public static boolean isSymmetric(TreeNode root) {
+        return isSymmetric(root, root);
+    }
+
+    private static boolean isSymmetric(TreeNode p, TreeNode q) {
+        if (p == null && q == null) {
+            return true;
+        }
+        if (p == null || q == null) {
+            return false;
+        }
+        if (p.val != q.val) {
+            return false;
+        }
+        boolean one = isSymmetric(p.right, q.left);
+        boolean two = isSymmetric(p.left, q.right);
+        return one && two;
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode102.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode102.java
new file mode 100644
index 0000000..038bffb
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode102.java
@@ -0,0 +1,68 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import cn.whaifree.leetCode.model.TreeNode;
+
+import java.util.*;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/25 22:45
+ * @注释
+ */
+public class LeetCode102 {
+    public static void main(String[] args) {
+
+        TreeNode treeNode = TreeNode.constructTreeByArray(3, 9, 20, null, null, 15, 7);
+        for (List<Integer> integers : levelOrder1(treeNode)) {
+            System.out.println(integers);
+        }
+    }
+
+    public static List<List<Integer>> levelOrder(TreeNode root) {
+
+        List<List<Integer>> res = new ArrayList<>();
+        if (root == null) {
+            return res;
+        }
+        Deque<TreeNode> deque = new LinkedList<>();
+        deque.add(root);
+        while (!deque.isEmpty()) {
+            int size = deque.size();
+            List<Integer> list = new ArrayList<>();
+            for (int i = 0; i < size; i++) {
+                TreeNode pop = deque.pop();
+                list.add(pop.val);
+                if (pop.left != null) {
+                    deque.add(pop.left);
+                }
+                if (pop.right != null) {
+                    deque.add(pop.right);
+                }
+            }
+            res.add(list);
+        }
+
+
+        return res;
+    }
+
+    public static List<List<Integer>> levelOrder1(TreeNode root) {
+        List<List<Integer>> res = new ArrayList<>();
+        level(root, 0, res);
+        return res;
+    }
+
+    public static void level(TreeNode root, int inLevel, List<List<Integer>> res) {
+        if (root == null) {
+            return;
+        }
+        if (res.size() == inLevel) {
+            res.add(new ArrayList<>());
+        }
+        res.get(inLevel).add(root.val);
+        level(root.left, inLevel + 1, res);
+        level(root.right, inLevel + 1, res);
+    }
+
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode105.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode105.java
new file mode 100644
index 0000000..3238bfc
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode105.java
@@ -0,0 +1,64 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import cn.whaifree.leetCode.model.TreeNode;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/28 18:31
+ * @注释
+ */
+public class LeetCode105 {
+
+    public static void main(String[] args) {
+//        int[] preorder = {3, 9, 20, 15, 7};
+//        int[] inorder = {9, 3, 15, 20, 7};
+//        TreeNode root = buildTree(preorder, inorder);
+//        root.printTree();
+//
+//        TreeNode treeNode = buildTree(new int[]{1}, new int[]{1});
+//        TreeNode.printTree(treeNode);
+
+        buildTree(new int[]{1,2,3}, new int[]{3,2,1}).printTree();
+    }
+
+    /**
+     *
+     *
+     * @param preorder {3, 9, 20, 15, 7}
+     * @param inorder {9, 3, 15, 20, 7}
+     * @return
+     */
+    public static TreeNode buildTree(int[] preorder, int[] inorder) {
+        return build(preorder, inorder, 0, preorder.length - 1, 0, inorder.length - 1);
+    }
+
+    public static TreeNode build(int[] preorder, int[] inorder, int preStart, int preEnd, int inStart, int inEnd) {
+        if (preStart > preEnd) {
+            return null;
+        }
+        if (preStart == preEnd) {
+            return new TreeNode(preorder[preStart]);
+        }
+        if (inStart == inEnd) {
+            return new TreeNode(inorder[inStart]);
+        }
+
+        // 前序中的第一个
+        int want = preorder[preStart];
+        // 在中序中找到分界的位置
+        int inorderIndex = 0;
+        for (int i = inStart; i <= inEnd; i++) {
+            if (inorder[i] == want) {
+                inorderIndex = i;
+                break;
+            }
+        }
+        // 这个节点中序的左边有几个节点
+        int leftInorderLen = inorderIndex - inStart;
+        TreeNode node = new TreeNode(want);
+        node.left = build(preorder, inorder, preStart + 1, preStart + leftInorderLen, inStart, inorderIndex - 1);
+        node.right = build(preorder, inorder, preStart + leftInorderLen + 1, preEnd, inorderIndex + 1, inEnd);
+        return node;
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode110.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode110.java
new file mode 100644
index 0000000..62515c7
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode110.java
@@ -0,0 +1,39 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import cn.whaifree.leetCode.model.TreeNode;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/28 0:23
+ * @注释
+ */
+public class LeetCode110 {
+
+    public static void main(String[] args) {
+
+        TreeNode treeNode = TreeNode.constructTreeByArray(1, 2, 2, 3, 3, null, null, 4, 4);
+//        System.out.println(isBalanced(treeNode));
+        System.out.println(isBalanced(TreeNode.constructTreeByArray(1,2,2,3,null,null,3,4,null,null,4)));
+    }
+    public static boolean isBalanced(TreeNode root) {
+        if (root == null) {
+            return true;
+        }
+        return level(root) != -1;
+    }
+
+    public static int level(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        int left = level(root.left);
+        if (left==-1) return -1;
+        int right = level(root.right);
+        if (right==-1) return -1;
+        if (Math.abs(left - right) > 1) {
+            return -1;
+        }
+        return Math.max(left, right) + 1;
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode216.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode216.java
new file mode 100644
index 0000000..990cc9c
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode216.java
@@ -0,0 +1,48 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/28 21:46
+ * @注释
+ */
+public class LeetCode216 {
+    public static void main(String[] args) {
+        System.out.println(combinationSum3(9, 45));
+    }
+    static List<List<Integer>> res = new ArrayList<>();
+    static List<Integer> path = new ArrayList<>();
+    static int nowSum = 0;
+    public static List<List<Integer>> combinationSum3(int k, int n) {
+        circle(k, n, 1);
+        return res;
+    }
+
+    public static void circle(int k, int n, int start) {
+        if (nowSum == n && path.size() == k) {
+            res.add(new ArrayList<>(path));
+            return;
+        }
+
+        for (int i = start; i <= 9; i++) {
+            /**
+             * nowSum + i > n
+             * path.size+9-i>k
+             */
+            if (nowSum + i > n) {
+                break;
+            }
+            if ((9 - i + 1) < k - path.size()) {
+                break;
+            }
+            nowSum += i;
+            path.add(i);
+            circle(k, n, i + 1);
+            path.remove(path.size() - 1);
+            nowSum -= i;
+        }
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode222.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode222.java
new file mode 100644
index 0000000..6668d0e
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode222.java
@@ -0,0 +1,46 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import cn.whaifree.leetCode.model.TreeNode;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/28 19:40
+ * @注释
+ */
+public class LeetCode222 {
+    public static void main(String[] args) {
+        System.out.println(countNodes(TreeNode.constructTreeByArray(1, 2, 3, 4, 5, 6)));
+    }
+
+    public static int countNodes(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        return count(root);
+    }
+
+    public static int count(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+
+        TreeNode i = root;
+        int leftDepth = 0;
+        while (i.left != null) {
+            i = i.left;
+            leftDepth++;
+        }
+        i = root;
+        int rightDepth = 0;
+        while (i.right != null) {
+            i = i.right;
+            rightDepth++;
+        }
+        if (leftDepth == rightDepth) {
+            return (2 << leftDepth) - 1;
+        }else {
+            return count(root.left) + count(root.right) + 1;
+        }
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode232.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode232.java
new file mode 100644
index 0000000..457e035
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode232.java
@@ -0,0 +1,67 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import java.util.Deque;
+import java.util.LinkedList;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/24 22:17
+ * @注释
+ */
+public class LeetCode232 {
+
+    public static void main(String[] args) {
+        MyQueue myQueue = new MyQueue();
+        myQueue.push(1); // queue is: [1]
+        myQueue.push(2); // queue
+        System.out.println(myQueue.peek());
+        System.out.println(myQueue.pop());
+        System.out.println(myQueue.empty());
+        System.out.println(myQueue.pop());
+        System.out.println(myQueue.empty());
+    }
+
+    static class MyQueue {
+
+        Deque<Integer> stack1;
+        Deque<Integer> stack2;
+
+        public MyQueue() {
+            stack1 = new LinkedList<>();
+            stack2 = new LinkedList<>();
+        }
+
+        public void push(int x) {
+            stack1.push(x);
+        }
+
+        public int pop() {
+            while (stack1.size() > 1) {
+                stack2.push(stack1.pop());
+            }
+            int res = stack1.pop();
+            while (!stack2.isEmpty()) {
+                stack1.push(stack2.pop());
+            }
+            return res;
+        }
+
+        public int peek() {
+            while (stack1.size() > 1) {
+                stack2.push(stack1.pop());
+            }
+            int res = stack1.pop();
+            stack2.push(res);
+            while (!stack2.isEmpty()) {
+                stack1.push(stack2.pop());
+            }
+            return res;
+        }
+
+        public boolean empty() {
+            return stack1.isEmpty();
+        }
+    }
+
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode236.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode236.java
new file mode 100644
index 0000000..c71d376
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode236.java
@@ -0,0 +1,34 @@
+package cn.whaifree.redo.redo_all_240721;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/28 20:43
+ * @注释
+ */
+
+import cn.whaifree.leetCode.model.TreeNode;
+
+public class LeetCode236 {
+    public static void main(String[] args) {
+        TreeNode treeNode = TreeNode.constructTreeByArray(3, 5, 1, 6, 2, 0, 8, null, null, 7, 4);
+        lowestCommonAncestor(treeNode, new TreeNode(6), new TreeNode(4)).printTree();
+    }
+    public static TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        if (root == null || root.val == p.val || root.val == q.val) {
+            return root;
+        }
+        TreeNode right = lowestCommonAncestor(root.right, p, q);
+        TreeNode left = lowestCommonAncestor(root.left, p, q);
+        if (right == null && left == null) {
+            return null;
+        }
+        if (right != null && left != null) {
+            return root;
+        } if (right != null) {
+            return right;
+        } else {
+            return left;
+        }
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode257.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode257.java
new file mode 100644
index 0000000..6595751
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode257.java
@@ -0,0 +1,56 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import cn.whaifree.leetCode.model.TreeNode;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/28 0:32
+ * @注释
+ */
+public class LeetCode257 {
+    public static void main(String[] args) {
+        TreeNode treeNode = TreeNode.constructTreeByArray(3, 9, 20, null, null, 15, 7);
+        for (String binaryTreePath : binaryTreePaths(treeNode)) {
+            System.out.println(binaryTreePath);
+        }
+        for (String binaryTreePath : binaryTreePaths(TreeNode.constructTreeByArray(1,2,3,null,null,4,5))) {
+            System.out.println(binaryTreePath);
+        }
+    }
+
+    public static List<String> binaryTreePaths(TreeNode root) {
+        List<String> res = new ArrayList<>();
+        List<Integer> path = new ArrayList<>();
+        search(root, res, path);
+        return res;
+    }
+
+    public static void search(TreeNode root,List<String> res, List<Integer> path) {
+        if (root == null) {
+            return;
+        }
+        path.add(root.val);
+        if (root.left == null && root.right == null) {
+            int val = root.val;
+            StringBuilder stringBuilder = new StringBuilder();
+            for (int i = 0; i < path.size() - 1; i++) {
+                stringBuilder.append(path.get(i)).append("->");
+            }
+            stringBuilder.append(val);
+            res.add(stringBuilder.toString());
+        }
+        if (root.right != null) {
+            search(root.right,  res, path);
+        }
+        if (root.left != null) {
+            search(root.left, res, path);
+        }
+        path.remove(path.size() - 1);
+    }
+
+
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode347.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode347.java
new file mode 100644
index 0000000..5c09548
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode347.java
@@ -0,0 +1,46 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import java.util.*;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/24 22:23
+ * @注释
+ */
+public class LeetCode347 {
+    public static void main(String[] args) {
+        int[] nums = {1,1,1,2,2,3};
+        int k = 2;
+        int[] ints = topKFrequent(nums, k);
+        System.out.println(Arrays.toString(ints));
+    }
+
+    public static int[] topKFrequent(int[] nums, int k) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int num : nums) {
+            map.put(num, map.getOrDefault(num, 0) + 1);
+        }
+
+        PriorityQueue<Integer> priorityQueue = new PriorityQueue<Integer>(
+                new Comparator<Integer>() {
+                    @Override
+                    public int compare(Integer o1, Integer o2) {
+                        if (map.get(o1) > map.get(o2)) {
+                            return -1;
+                        }else {
+                            return 1;
+                        }
+                    }
+                }
+        );
+
+        priorityQueue.addAll(map.keySet());
+
+        ArrayList<Integer> res = new ArrayList<>();
+        for (int i = 0; i < k; i++) {
+            res.add(priorityQueue.poll());
+        }
+        return res.stream().mapToInt(Integer::intValue).toArray();
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode77.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode77.java
new file mode 100644
index 0000000..ff3c84c
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode77.java
@@ -0,0 +1,50 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/28 20:26
+ * @注释
+ */
+public class LeetCode77
+{
+
+    public static void main(String[] args)
+    {
+        int n = 4;
+        int k = 2;
+        System.out.println(new LeetCode77().combine(n, k));
+    }
+
+    List<List<Integer>> res = new ArrayList<>();
+    List<Integer> path = new ArrayList<>();
+    public  List<List<Integer>> combine(int n, int k)
+    {
+        circle(n, 1, k);
+        return res;
+    }
+
+    public void circle(int n, int start, int k) {
+        if (path.size() == k) {
+            res.add(new ArrayList<>(path));
+            return;
+        }
+        /**
+         * n start k i
+         * 能够提供的数 n-i
+         * 还需要的数 k - path.size
+         */
+        for (int i = start; i <= n; i++) {
+            // 剪枝
+            if (n - i < k - path.size() - 1) {
+                break;
+            }
+            path.add(i);
+            circle(n, i + 1, k);
+            path.remove(path.size() - 1);
+        }
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode94.java b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode94.java
new file mode 100644
index 0000000..093f682
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/redo_all_240721/LeetCode94.java
@@ -0,0 +1,58 @@
+package cn.whaifree.redo.redo_all_240721;
+
+import cn.whaifree.leetCode.model.TreeNode;
+
+import java.util.Deque;
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/7/24 22:37
+ * @注释
+ */
+public class LeetCode94 {
+
+
+    public static void main(String[] args) {
+        TreeNode treeNode = TreeNode.constructTreeByArray();
+        List<Integer> integers = inorderTraversal(treeNode);
+        for (Integer integer : integers) {
+            System.out.println(integer);
+        }
+    }
+
+
+    /**
+     *
+     * @param root
+     * @return
+     */
+    public static List<Integer> inorderTraversal(TreeNode root) {
+
+        List<Integer> res = new LinkedList<>();
+        if (root == null) {
+            return res;
+        }
+        Deque<TreeNode> stack = new LinkedList<>();
+        stack.add(root);
+        while (!stack.isEmpty()) {
+            TreeNode pop = stack.pop();
+            if (pop != null) {
+                if (pop.right != null) {
+                    stack.push(pop.right);
+                }
+                stack.push(pop);
+                stack.push(null);
+                if (pop.left != null) {
+                    stack.push(pop.left);
+                }
+            }else {
+                res.add(stack.pop().val);
+            }
+
+        }
+        return res;
+    }
+}