贪心

src/main/java/cn/whaifree/leetCode/Greedy/LeetCode1005.java

@@ -0,0 +1,113 @@
+package cn.whaifree.leetCode.Greedy;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.stream.IntStream;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/2/27 11:42
+ * @注释
+ */
+public class LeetCode1005 {
+
+    @Test
+    public void test() {
+        System.out.println(new Solution().largestSumAfterKNegations(new int[]{-2,5,0,2,-2}, 3));
+        System.out.println(new Solution().largestSumAfterKNegations(new int[]{4,2,3}, 1))
+        ;
+
+        System.out.println(new Solution1().largestSumAfterKNegations(new int[]{-2,5,0,2,-2}, 3));
+        System.out.println(new Solution1().largestSumAfterKNegations(new int[]{4,2,3}, 1));
+    }
+
+
+    class Solution {
+
+        /**
+         * 注意几个例子
+         * 1. nums = [3,-1,0,2], k = 3   选择下标 (1, 2, 2) ，nums 变为 [3,1,0,2]
+         *
+         * -2,5,1,2,-2
+         * 按绝对值逆转   5 -2 2 -2 1
+         * 每次遇到负数，变为相反数
+         * // 剩下的k如果是奇数，就把最后一个逆转
+         *
+         * @param nums
+         * @param k
+         * @return
+         */
+        public int largestSumAfterKNegations(int[] nums, int k) {
+            // 按绝对值从大到小排序，对前k个负数进行相反数
+            nums = IntStream.of(nums)
+                    .boxed()
+                    .sorted((o1, o2) -> Math.abs(o2) - Math.abs(o1))
+                    .mapToInt(Integer::intValue).toArray();
+
+
+            for (int i = 0; i < nums.length; i++) {
+                if (k > 0 && nums[i] < 0) {
+                    nums[i] = -nums[i];
+                    k--;
+                }
+            }
+
+            // 此时还有k个没减去,k为偶数则不管，k为奇数就把最小那个变为正数
+            if (k % 2 == 1) {
+                nums[nums.length-1] = -nums[nums.length-1];
+            }
+
+
+            return Arrays.stream(nums).sum();
+        }
+    }
+
+    class Solution1 {
+
+        /**
+         * 注意几个例子
+         * 1. nums = [3,-1,0,2], k = 3   选择下标 (1, 2, 2) ，nums 变为 [3,1,0,2]
+         *
+         * -2,5,1,2,-2
+         * 排序
+         * -2 -2 1 2 5
+         * 逆转
+         * 2 2 1 2 5
+         * 将最下的数逆转,sum-min-min
+         * 2 2 -1 2 5
+         *
+         * @param nums
+         * @param k
+         * @return
+         */
+        public int largestSumAfterKNegations(int[] nums, int k) {
+            // 按绝对值从大到小排序，对前k个负数进行相反数
+            Arrays.sort(nums);
+
+
+            int sum = 0;
+            int minValue = Integer.MAX_VALUE;
+            for (int i = 0; i < nums.length; i++) {
+                if (k > 0 && nums[i] < 0) {
+                    nums[i] = -nums[i];
+                    k--;
+                }
+                sum += nums[i];
+                minValue = Math.min(minValue, nums[i]);
+            }
+
+            // 此时还有k个没减去,k为偶数则不管，k为奇数就把最小那个变为正数
+            if (k % 2 == 1) {
+                // 减去在遍历过程中加的minValue部分和通过变换负数的部分
+                return sum - minValue - minValue;
+            }else {
+                return sum;
+            }
+
+        }
+    }
+
+}

src/main/java/cn/whaifree/leetCode/Greedy/LeetCode134.java

@@ -0,0 +1,105 @@
+package cn.whaifree.leetCode.Greedy;
+
+import org.junit.Test;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/2/27 20:02
+ * @注释
+ */
+public class LeetCode134 {
+
+    @Test
+    public void test() {
+        System.out.println(new Solution().canCompleteCircuit(
+                new int[]{5,1,2,3,4},
+                new int[]{4,4,1,5,1}
+        ));
+
+    }
+
+    class Solution {
+        /**
+         *
+         * @param gas 加油站有的油
+         * @param cost 行驶代价
+         * @return
+         */
+        public int canCompleteCircuit(int[] gas, int[] cost) {
+
+            int[] rent = new int[gas.length];
+            int total = 0;
+            for (int i = 0; i < gas.length; i++) {
+                rent[i] = gas[i] - cost[i];
+                total += rent[i];
+            }
+            // 如果全部剩余<0 则必然跑不了一圈
+            if (total < 0) {
+                return -1;
+            }
+
+
+            // 以下为必然可以跑一圈的
+            // 如果当前剩余不够用，则让指针指向i+1
+            int curSum = 0;
+            int index = 0;
+            for (int i = 0; i < rent.length; i++) {
+                curSum += rent[i];
+                if (curSum < 0) {
+                    index = (i + 1) % gas.length ;
+                    curSum = 0;
+                }
+            }
+            // 1. 前提，必然能跑一圈
+            // 2. 没有进入某个i之后都没有curSum<0 那么就是正确的i
+            return index;
+        }
+
+    }
+//    class Solution {
+//        /**
+//         *
+//         * @param gas 加油站有的油
+//         * @param cost 行驶代价
+//         * @return
+//         */
+//        public int canCompleteCircuit(int[] gas, int[] cost) {
+//            int needSum = 0;
+//            for (int i : cost) {
+//                needSum += i;
+//            }
+//
+//            int iHave = 0;
+//            int sumAdd = 0;
+//            int start = 0;
+//            for (int i = 0; i < gas.length; i++) {
+//                iHave += gas[i];
+//                sumAdd += gas[i];
+//                if (iHave < cost[i]) {
+//                    iHave = 0;
+//                    i = start;
+//                    start = start + 1;
+//                    sumAdd = 0;
+//                    continue;
+//                }
+//                iHave -= cost[i];
+//                if (sumAdd >= needSum) {
+//                    return start;
+//                }
+//
+//                if (i == gas.length - 1) {
+//                    i = -1;
+//                }
+//
+//                if (start == gas.length - 1 && start != i) {
+//                    break;
+//                }
+//            }
+//
+//            return -1;
+//        }
+//
+//    }
+
+}

src/main/java/cn/whaifree/leetCode/Greedy/LeetCode135.java

@@ -0,0 +1,63 @@
+package cn.whaifree.leetCode.Greedy;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Vector;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/2/28 12:44
+ * @注释
+ */
+public class LeetCode135 {
+
+    @Test
+    public void tesr() {
+        System.out.println(new Solution().candy(new int[]{1, 2, 2, 5, 4, 3, 2}));
+    }
+
+
+    class Solution {
+        public int candy(int[] ratings) {
+            // 从前往后遍历，遇到ratings[i]>ratings[i-1] score[i]+1
+            int length = ratings.length;
+
+            int[] scores = new int[length];
+            scores[0] = 1;
+
+            for (int i = 1; i < length; i++) {
+                if (ratings[i] > ratings[i - 1]) {
+                    scores[i] = scores[i - 1] + 1;
+                }else {
+                    scores[i] = 1;
+                }
+            }
+
+            // 从后往前
+            for (int i = length -1; i > 0; i--) {
+                /**
+                 * 如果 ratings[i] < ratings[i - 1]，此时candyVec[i-1]（第i-1个小孩的糖果数量）就有两个选择了，
+                 * -  一个是candyVec[i] + 1（从右边这个加1得到的糖果数量），
+                 * -  一个是candyVec[i-1]（之前比较右孩子大于左孩子得到的糖果数量）。
+                 * 如 5 3
+                 *    从右边向左边，i-1可选择为 3+1 或者原来的 5，从左往右已经处理过的，
+                 *      同时要满足同时保证i小孩既大于左也大于右边，那么取最大值。
+                 * 同时保证i小孩既大于左也大于右边
+                 */
+                if (ratings[i] < ratings[i - 1]) {
+                    scores[i - 1] = Math.max(scores[i] + 1, scores[i - 1]);
+                }
+            }
+
+            int scoreSum = 0;
+            for (int score : scores) {
+                scoreSum += score;
+            }
+
+            return scoreSum;
+        }
+    }
+
+}

src/main/java/cn/whaifree/leetCode/Greedy/LeetCode45.java

@@ -0,0 +1,102 @@
+package cn.whaifree.leetCode.Greedy;
+
+import org.junit.Test;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/2/27 11:01
+ * @注释
+ */
+public class LeetCode45 {
+
+    @Test
+    public void test() {
+        System.out.println(new Solution().jump(new int[]{2,3,1,1,4}));
+    }
+
+    class Solution {
+        /**
+         * 每个区间内只有一个最跳数
+         * 每个区间只增加一次jump
+         * 1. 标记临时最大区间
+         * 2. 标记区间结束时jump++
+         * @param nums
+         * @return
+         */
+        public int jump(int[] nums) {
+
+            // 最远覆盖范围能否到达nums.length-1
+
+            if (nums.length == 1) {
+                return 0;
+            }
+
+            // 最大覆盖范围
+            int maxCover = 0;
+
+            // 当前index覆盖范围区间
+            int curInterval = 0;
+            int jumpCount = 0;
+            for (int i = 0; i < nums.length; i++) {
+                // 当前最大覆盖区间
+                maxCover = Math.max(maxCover, i + nums[i]);
+
+                // 必须等待区间增加后再判断是否到末位
+                if (maxCover >= nums.length - 1) {
+                    jumpCount++;
+                    break;
+                }
+
+                // 如果到了当前index覆盖的区间最后一个
+                if (i ==  curInterval) {
+                    jumpCount++;
+                    curInterval = maxCover;
+
+                }
+
+
+            }
+            return jumpCount;
+        }
+    }
+
+    class Solution1 {
+        /**
+         * 每个区间内只有一个最跳数
+         * 每个区间只增加一次jump
+         * 1. 标记临时最大区间
+         * 2. 到达最大跳数++
+         * @param nums
+         * @return
+         */
+        public int jump(int[] nums) {
+
+            // 最远覆盖范围能否到达nums.length-1
+
+            if (nums.length == 1) {
+                return 0;
+            }
+
+            // 最大覆盖范围
+            int maxCover = 0;
+
+            // 当前index覆盖范围区间
+            int curInterval = 0;
+            int jumpCount = 0;
+            for (int i = 0; i < nums.length - 1; i++) {
+                // if (nextDistance >= nums.size() - 1) break;
+                // 让nums.length变成num.length-1 本质是一样的
+
+                // 当前最大覆盖区间
+                maxCover = Math.max(maxCover, i + nums[i]);
+                if (i == curInterval) {
+                    jumpCount++;
+                    curInterval = maxCover;
+                }
+            }
+            return jumpCount;
+        }
+    }
+
+}

src/main/java/cn/whaifree/leetCode/Greedy/LeetCode55.java

@@ -0,0 +1,75 @@
+package cn.whaifree.leetCode.Greedy;
+
+import cn.whaifree.leetCode.Tree.LeetCode94;
+import org.junit.Test;
+import sun.misc.Launcher;
+
+import java.net.URL;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/2/26 11:33
+ * @注释
+ */
+public class LeetCode55 {
+
+    @Test
+    public void test() {
+        System.out.println(new Solution().canJump(new int[]{2,0,0}));
+
+
+
+    }
+
+
+
+
+
+    class CustomClassLoader extends ClassLoader {
+        public CustomClassLoader(ClassLoader parent) {
+            super(parent);
+        }
+
+        @Override
+        protected Class<?> findClass(String name) throws ClassNotFoundException {
+            byte[] res = getClassFromCustomClass(name);
+            if (res != null) {
+                return defineClass(name, res, 0, res.length);
+            } else {
+                throw new ClassNotFoundException(name);
+            }
+        }
+
+        private byte[] getClassFromCustomClass(String name) {
+            //自定义路径加载指定类
+            // 加密解密
+            return null;
+        }
+    }
+
+    class Solution {
+        /**
+         * 每个index都有一个cover覆盖范围，一旦这个范围可以覆盖nums，就能够返回
+         * @param nums
+         * @return
+         */
+        public boolean canJump(int[] nums) {
+            if (nums.length == 1) {
+                return true;
+            }
+
+            // cover表示最远能到哪里
+            int cover = 0;
+            // 注意这里cover表示能够覆盖的最远范围，不能超过他
+            for (int i = 0; i <= cover; i++) {
+                cover = Math.max(i + nums[i], cover);
+                if (cover >= nums.length - 1) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+    }
+}

src/main/java/cn/whaifree/leetCode/Greedy/LeetCode860.java

@@ -0,0 +1,58 @@
+package cn.whaifree.leetCode.Greedy;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/2/28 13:22
+ * @注释
+ */
+public class LeetCode860 {
+
+    @Test
+    public void test() {
+        System.out.println(new Solution().lemonadeChange(new int[]{5,5,10,10,20}));
+    }
+
+    class Solution {
+
+        /**
+         * bills[i] 不是 5 就是 10 或是 20
+         * @param bills
+         * @return
+         */
+        public boolean lemonadeChange(int[] bills) {
+
+            int fiveHave = 0; // 有5元的钞票数
+            int tenHave = 0; // 10元钞票数
+            for (int i = 0; i < bills.length; i++) {
+
+                if (bills[i] == 5) { // 5元直接收下
+                    fiveHave++;
+                } else if (bills[i] == 10) { // 10元则找5元
+                    tenHave++;
+                    fiveHave--;
+                } else if (bills[i] == 20) { // 20元可以选择给他10+5或者3个5元
+                    if (tenHave >= 1) {
+                        tenHave--;
+                        fiveHave--;
+                    } else {
+                        fiveHave -= 3;
+                    }
+                }
+                // 如果钞票不够找
+                if (fiveHave < 0 || tenHave < 0) {
+                    return false;
+                }
+            }
+            return true;
+        }
+
+
+    }
+}

src/main/java/cn/whaifree/leetCode/T.java

@@ -0,0 +1,102 @@
+package cn.whaifree.leetCode;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/2/27 17:58
+ * @注释
+ */
+public class T {
+
+    public int A() {
+        B();
+        return 1;
+    }
+
+    public void B() {
+
+    }
+}
+
+interface Animal {
+    void eat();
+}
+
+class Hunter{
+   void hunt() {
+
+   }
+}
+
+class Cat extends Hunter implements Animal {
+
+    @Override
+    void hunt() {
+        System.out.println("cat hunt");
+    }
+
+    @Override
+    public void eat() {
+        System.out.println("cat eat");
+    }
+}
+
+class Dog extends Hunter implements Animal {
+
+    public Dog() {
+        super();
+    }
+
+    public Dog(String name) {
+        super();
+    }
+
+    @Override
+    void hunt() {
+        System.out.println("dog hunt");
+    }
+
+    @Override
+    public void eat() {
+        System.out.println("dog eat");
+    }
+}
+
+class AnimalTest {
+    public static void main(String[] args) {
+        // 晚期绑定，动态链接
+        // 运行时才能确定
+        Animal animal = new Cat();
+        animal.eat();
+        Hunter hunter = (Hunter) animal;
+        hunter.hunt();
+
+        // 静态多态
+        Dog dog = new Dog("!23");
+
+
+    }
+}
+
+
+class Father{
+    public static void print(String str){
+        System. out. println("father "+str);
+    }
+    public void show(String str){
+        System. out. println("father"+str);
+    }
+}
+
+class Son extends Father {
+
+
+}
+
+class VirtualMethodTest {
+    public static void main(String[] args) {
+        Son.print("coder");
+        Father fa = new Father();
+        fa.show("a");
+    }
+}

src/main/java/cn/whaifree/leetCode/Test.java

@@ -11,66 +11,130 @@ import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
 /**
- *
  * 给定一个整数数组 nums 和一个整数目标值 target，请你在该数组中找出 和为目标值 target  的那 两个 整数，并返回它们的数组下标。
- *
+ * <p>
  * 你可以假设每种输入只会对应一个答案。但是，数组中同一个元素在答案里不能重复出现。
- *
+ * <p>
  * 你可以按任意顺序返回答案。
- *
+ * <p>
  * 来源：力扣（LeetCode）
  * 链接：https://leetcode.cn/problems/two-sum
  * 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
- *
+ * <p>
- *
+ * <p>
- *
+ * <p>
  * 输入：nums = [2,7,11,15], target = 9
  * 输出：[0,1]
  * 解释：因为 nums[0] + nums[1] == 9 ，返回 [0, 1] 。
  *
- *
  * @author whaifree
  * @package cn.whaifree.leetCode
  * @Date: 2022/9/13 20:54
  */
-public class Test  {
+public class Test {
+
+    private static int number;
+
+    private int getNumber;
 
 
-    static {
+    public int minus() {
-        num = 20;
+        localVarl();
-        // 防止在初始化前程序中访问默认值
+        int i = 1;
+        double d = 2d;
+        char c = 'd';
+        return (int) (i + d);
     }
-    private static int num = 10;
+
+    public void localVarl() {
+        int a = 0;
+        System.out.println(a);
+        int b = 0;
+    }
+
+    public void localVar2() {
+        {
+            int a = 0;
+            System.out.println(a);
+        }
+        //此时的就会复用a的槽位
+        int b = 0;
+    }
+
 
     public static void main(String[] args) {
-        ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
-        System.out.println(systemClassLoader);
 
-        ClassLoader extClassLoader = systemClassLoader.getParent();
+        //第1类问题
-        System.out.println(extClassLoader);
+        int i1 = 10;
-
+        i1++;
-        // 获取不到引导类类加载器
+        int i2 = 10;
-        ClassLoader bootClassLoader = extClassLoader.getParent();
+        ++i2;
-        System.out.println(bootClassLoader);
-
-        ClassLoader classLoader = Test.class.getClassLoader();
-        System.out.println(classLoader);
 
 
-        // 系统核心类库都是使用引导类（BootStrapClassLoader）进行加载，都为null
+        //第2类问题:
-        ClassLoader stringLoader = String.class.getClassLoader();
+        int i3 = 10;
-        System.out.println(stringLoader);
+        int i4 = i3++;
+        int i5 = 10;
+        int i6 = ++i5;
 
 
-        PriorityQueue<Integer> objects = new PriorityQueue<>();
+        //第3类问题:
-        objects.add(1);
+        int i7 = 10;
-        objects.add(2);
+        i7 = i7++;
-        objects.add(3);
+        int i8 = 10;
-        objects.add(4);
+        i8 = ++i8;
-        System.out.println(objects.poll());
+
-        System.out.println(objects.poll());
+        // 第四类问题
+        int i9 = 10;
+        int i10 = i9++ + ++i9;
+
+//        // 挨个输出i1-i10
+//        System.out.println(i1);
+//        System.out.println(i2);
+//        System.out.println(i3);
+//        System.out.println(i4);
+//        System.out.println(i5);
+//        System.out.println(i6);
+//        System.out.println(i7);
+//        System.out.println(i8);
+//        System.out.println(i9);
+//        System.out.println(i10);
+//
+//
+//
+//        System.out.println(new Test().getNumber);
+//
+//        System.out.println(Test.number);
+//        // 递归删除某个目录下所有文件名为(1)的文件
+//
+//
+//        ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
+//        System.out.println(systemClassLoader);
+//
+//        ClassLoader extClassLoader = systemClassLoader.getParent();
+//        System.out.println(extClassLoader);
+//
+//        // 获取不到引导类类加载器
+//        ClassLoader bootClassLoader = extClassLoader.getParent();
+//        System.out.println(bootClassLoader);
+//
+//        ClassLoader classLoader = Test.class.getClassLoader();
+//        System.out.println(classLoader);
+//
+//
+//        // 系统核心类库都是使用引导类（BootStrapClassLoader）进行加载，都为null
+//        ClassLoader stringLoader = String.class.getClassLoader();
+//        System.out.println(stringLoader);
+//
+//
+//        PriorityQueue<Integer> objects = new PriorityQueue<>();
+//        objects.add(1);
+//        objects.add(2);
+//        objects.add(3);
+//        objects.add(4);
+//        System.out.println(objects.poll());
+//        System.out.println(objects.poll());
 
 
     }
-
 }