2024/9/26 Hot100 dp结束

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

@@ -41,6 +41,7 @@ public class Num31 {
 
     /**
      * 动态规划解法
+     *
      * @param s
      * @return
      */
@@ -67,4 +68,46 @@ public class Num31 {
         }
         return max;
     }
+
+    /**
+     * 双指针
+     *
+     * @param s
+     * @return
+     */
+    public int longestValidParentheses3(String s) {
+        int left = 0, right = 0, max = 0;
+        //从前往后右括号大于左括号，left和right都归0
+        for (int i = 0; i < s.length(); i++) {
+            if (s.charAt(i) == '(') {
+                left++;
+            } else {
+                right++;
+            }
+            //left大于right先不管
+            if (left == right) {
+                max = Math.max(max, 2 * right);
+            } else if (right > left) {
+                //right大于left重新记
+                left = right = 0;
+            }
+        }
+        left = right = 0;
+        //从后往前左括号大于右括号，left和right都归0
+        for (int i = s.length() - 1; i >= 0; i--) {
+            if (s.charAt(i) == '(') {
+                left++;
+            } else {
+                right++;
+            }
+            if (left == right) {
+                max = Math.max(max, 2 * left);
+            } else if (left > right) {
+                //left大于right重新记,这个很重要
+                left = right = 0;
+            }
+        }
+        return max;
+    }
+
 }