diff --git a/src/main/java/cn/whaifree/redo/LeetCode15.java b/src/main/java/cn/whaifree/redo/LeetCode15.java
new file mode 100644
index 0000000..4bab475
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/LeetCode15.java
@@ -0,0 +1,59 @@
+package cn.whaifree.redo;
+
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class LeetCode15 {
+
+    @Test
+    public void test() {
+        int[] nums = {1,0,0};
+        List<List<Integer>> lists = new Solution().threeSum(nums);
+        System.out.println(lists);
+    }
+
+
+    class Solution {
+        public List<List<Integer>> threeSum(int[] nums) {
+
+            Arrays.sort(nums);
+
+            List<List<Integer>> lists = new ArrayList<>();
+            // 计算三个数的和
+            for (int i = 0; i < nums.length; i++) {
+//
+                if (i != 0 && nums[i - 1] == nums[i]) { // 第一次不进入循环，i!=0
+                    continue;
+                }
+
+                int left = i + 1;
+                int right = nums.length - 1;
+                while (left < right) {
+                    int sum = nums[left] + nums[right] + nums[i];
+                    if (sum > 0) {
+                        right--;
+                    } else if (sum < 0) {
+                        left++;
+                    } else {
+                        lists.add(Arrays.asList(nums[left], nums[right], nums[i]));
+                        left++;
+                        right--;
+                        while (left < right && nums[left] == nums[left - 1]) { // 去重，且避免数组都是一个数字的情况
+                            left++;
+                        }
+                        while (left < right && nums[right] == nums[right + 1]) { // 去重，且避免数组都是一个数字的情况
+                            right--;
+                        }
+
+                    }
+
+                }
+            }
+            return lists;
+        }
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/LeetCode202.java b/src/main/java/cn/whaifree/redo/LeetCode202.java
new file mode 100644
index 0000000..99694c6
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/LeetCode202.java
@@ -0,0 +1,43 @@
+package cn.whaifree.redo;
+
+import org.junit.Test;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class LeetCode202 {
+
+    @Test
+    public void test() {
+        System.out.println(new Solution().isHappy(2));
+    }
+
+    class Solution {
+        /**
+         * 无限循环
+         * @param n
+         * @return
+         */
+        public boolean isHappy(int n) {
+            Set<Integer> set = new HashSet<>();
+            while (n != 1) {
+                if (set.contains(n)) {
+                    return false;
+                }
+                set.add(n);
+                n = get(n);
+            }
+            return true;
+        }
+
+        public int get(int n) {
+            int sum = 0;
+            while (n != 0) {
+                int e = n % 10;
+                sum += e * e;
+                n /= 10;
+            }
+            return sum;
+        }
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/LeetCode2487.java b/src/main/java/cn/whaifree/redo/LeetCode2487.java
new file mode 100644
index 0000000..7fded65
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/LeetCode2487.java
@@ -0,0 +1,62 @@
+package cn.whaifree.redo;
+
+import cn.whaifree.leetCode.model.ListNode;
+import org.junit.Test;
+
+public class LeetCode2487 {
+
+    @Test
+    public void test() {
+        ListNode head = ListNode.listNodeFromArray(new int[]{5, 2, 13, 3, 8});
+        ListNode reverse = new Solution().removeNodes(head);
+        reverse.printList();
+
+    }
+
+    /**
+     *
+     * 移除每个右侧有一个更大数值的节点。
+     * [5,2,13,3,8]
+     * 输出：[13,8]
+     *
+     * - 递减的
+     *
+     *
+     *
+     */
+    class Solution {
+        public ListNode removeNodes(ListNode head) {
+            // 逆转 8 3 13 2 5
+            head = reverse(head);
+            // 删除全部比当前点小的值
+            ListNode index = head;
+            ListNode maxNode = head;
+            while (index.next != null) {
+                if (maxNode.val > index.next.val) {
+                    index.next = index.next.next;
+                } else {
+                    index = index.next;
+                    maxNode = index;
+                }
+            }
+
+            return head;
+        }
+
+
+        // 1 2 3 4 5
+        public ListNode reverse(ListNode head) {
+            ListNode pre = null;
+            ListNode index = head;
+            ListNode tmp = null;
+            while (index != null) {
+                tmp = index.next;
+                index.next = pre;
+                pre = index;
+                index = tmp;
+            }
+            return pre;
+        }
+
+    }
+}
diff --git a/src/main/java/cn/whaifree/redo/LeetCode287.java b/src/main/java/cn/whaifree/redo/LeetCode287.java
new file mode 100644
index 0000000..61df1fd
--- /dev/null
+++ b/src/main/java/cn/whaifree/redo/LeetCode287.java
@@ -0,0 +1,51 @@
+package cn.whaifree.redo;
+
+import cn.hutool.core.lang.hash.Hash;
+import org.junit.Test;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class LeetCode287 {
+
+    @Test
+    public void test() {
+        System.out.println(new Solution().findDuplicate(new int[]{1, 3, 4, 3, 2}));
+    }
+
+    class Solution {
+        /**
+         * 要求 O（N）的时间复杂度
+         *     O（1）的控空间
+         *
+         *     将数组转换为链表的思想，即求有没有形成环
+         *     1 3 4 2 2
+         *     0 1 2 3 4
+         *  0-->1-->2-->4--->2
+         *
+         * @param nums
+         * @return
+         */
+        public int findDuplicate(int[] nums) {
+            // 1. 找到相遇的点
+            // 2. 将快指针指向首部
+            // 3. 两个指针重合处就是
+
+            int fast = 0;
+            int slow = 0;
+
+            do {
+                fast = nums[nums[fast]];
+                slow = nums[slow];
+            } while (fast != slow);
+
+            fast = 0;
+            while (fast != slow) {
+                fast = nums[fast];
+                slow = nums[slow];
+            }
+
+            return fast;
+        }
+    }
+}