2024/9/26 Hot100 dp结束，以及今日的每日一题

src/main/java/com/cool/hot100/dp/Num31.java

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+package com.cool.hot100.dp;
+
+import java.util.Stack;
+
+/**
+ * Created with IntelliJ IDEA.
+ *
+ * @Author: Cool
+ * @Date: 2024/09/26/13:53
+ * DayNumber 3
+ * Hard 3
+ * Level 7
+ * @Description 32. 最长有效括号
+ * @Link https://leetcode.cn/problems/longest-valid-parentheses/description/?envType=study-plan-v2&envId=top-100-liked
+ */
+public class Num31 {
+    /**
+     * 栈解法
+     *
+     * @param s
+     * @return
+     */
+    public int longestValidParentheses(String s) {
+        Stack<Integer> stack = new Stack<>();
+        int res = 0;
+        stack.push(-1);
+        for (int i = 0; i < s.length(); i++) {
+            if (s.charAt(i) == '(') {
+                stack.push(i);
+            } else {
+                stack.pop();
+                if (stack.empty()) {
+                    stack.push(i);
+                } else {
+                    res = Math.max(res, i - stack.peek());
+                }
+            }
+        }
+        return res;
+    }
+
+    /**
+     * 动态规划解法
+     * @param s
+     * @return
+     */
+    public int longestValidParentheses2(String s) {
+        int max = 0;
+        s = "a " + s;
+        int[] dp = new int[s.length()];
+        for (int i = 2; i < s.length(); i++) {
+            if (s.charAt(i) == ')') {
+                //s.charAt(i - dp[i - 1] - 1) == '('是在校验当前已组成有效括号的前一个括号是否为(,
+                max = Math.max(max, dp[i]);
+                if (s.charAt(i - 1) == ')') {
+                    if (s.charAt(i - dp[i - 1] - 1) == '(') {
+                        dp[i] = dp[i - 1] + 2 + dp[i - dp[i - 1] - 2];
+                    }
+                } else if (s.charAt(i - dp[i - 1] - 1) == '(') {
+                    /*i-2-dp[i-1]为当前已经组成有效括号的前一个括号,这里的有效括号与
+                    上面的有效括号不同，这里是算上当前括号的有效括号，用来应对()(())这样的数据*/
+                    dp[i] = dp[i - 2 - dp[i - 1]] + 2 + dp[i - 1];
+
+                }
+            }
+
+        }
+        return max;
+    }
+}

src/main/java/com/cool/hot100/dp/Num416.java

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+package com.cool.hot100.dp;
+
+import org.junit.Test;
+
+/**
+ * Created with IntelliJ IDEA.
+ *
+ * @Author: Cool
+ * @Date: 2024/09/26/09:31
+ * DayNumber 1
+ * Hard 2
+ * Level ?
+ * @Description 416. 分割等和子集
+ * @Link https://leetcode.cn/problems/partition-equal-subset-sum/description/?envType=study-plan-v2&envId=top-100-liked
+ */
+public class Num416 {
+    public boolean canPartition(int[] nums) {
+        int average = 0;
+        for (int num : nums) {
+            average += num;
+        }
+        if ((average & 1) == 1) {
+            return false;
+        }
+        average = average / 2;
+        boolean[] dp = new boolean[average + 1];
+        if (nums[0] <= average) {
+            dp[nums[0]] = true;
+        }
+        for (int i = 1; i < nums.length; i++) {
+            for (int j = average; nums[i] <= j; j--) {
+                dp[j] = dp[j] || dp[j - nums[i]];
+                if (dp[average]) {
+                    return true;
+                }
+            }
+        }
+        return dp[average];
+    }
+
+    @Test
+    public void test(){
+        canPartition(new int[]{1,2,5});
+    }
+}

src/main/java/com/cool/one_question_per_day/LeetCode20240926.java

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+package com.cool.one_question_per_day;
+
+/**
+ * Created with IntelliJ IDEA.
+ *
+ * @Author: Cool
+ * @Date: 2024/09/26/11:33
+ * DayNumber 2
+ * Hard 1
+ * Level ?
+ * @Description 2535. 数组元素和与数字和的绝对差
+ * @Link https://leetcode.cn/problems/difference-between-element-sum-and-digit-sum-of-an-array/description/?envType=daily-question&envId=2024-09-26
+ */
+public class LeetCode20240926 {
+    public int differenceOfSum(int[] nums) {
+        int sum=0;
+        int sum1=0;
+        for(int num:nums){
+            sum+=num;
+            while(num!=0){
+                sum1+=num%10;
+                num=num/10;
+            }
+        }
+        return Math.abs(sum1-sum);
+
+    }
+}