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package class14;
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public class Code01_Parentheses {
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public static boolean valid(String s) {
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char[] str = s.toCharArray();
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int count = 0;
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for (int i = 0; i < str.length; i++) {
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count += str[i] == '(' ? 1 : -1;
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if (count < 0) {
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return false;
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}
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}
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return count == 0;
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}
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public static int needParentheses(String s) {
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char[] str = s.toCharArray();
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int count = 0;
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int need = 0;
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for (int i = 0; i < str.length; i++) {
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if (str[i] == '(') {
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count++;
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} else { // 遇到的是')'
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if (count == 0) {
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need++;
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} else {
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count--;
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}
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}
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}
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return count + need;
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}
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public static boolean isValid(char[] str) {
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if (str == null || str.length == 0) {
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return false;
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}
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int status = 0;
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for (int i = 0; i < str.length; i++) {
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if (str[i] != ')' && str[i] != '(') {
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return false;
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}
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if (str[i] == ')' && --status < 0) {
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return false;
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}
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if (str[i] == '(') {
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status++;
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}
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}
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return status == 0;
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}
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public static int deep(String s) {
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char[] str = s.toCharArray();
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if (!isValid(str)) {
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return 0;
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}
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int count = 0;
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int max = 0;
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for (int i = 0; i < str.length; i++) {
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if (str[i] == '(') {
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max = Math.max(max, ++count);
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} else {
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count--;
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}
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}
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return max;
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}
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// s只由(和)组成
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// 求最长有效括号子串长度
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// 本题测试链接 : https://leetcode.com/problems/longest-valid-parentheses/
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public static int longestValidParentheses(String s) {
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if (s == null || s.length() < 2) {
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return 0;
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}
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char[] str = s.toCharArray();
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// dp[i] : 子串必须以i位置结尾的情况下，往左最远能扩出多长的有效区域
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int[] dp = new int[str.length];
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// dp[0] = 0; （ ）
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int pre = 0;
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int ans = 0;
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for (int i = 1; i < str.length; i++) {
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if (str[i] == ')') {
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// 当前谁和i位置的)，去配！
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pre = i - dp[i - 1] - 1; // 与str[i]配对的左括号的位置 pre
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if (pre >= 0 && str[pre] == '(') {
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dp[i] = dp[i - 1] + 2 + (pre > 0 ? dp[pre - 1] : 0);
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}
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}
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ans = Math.max(ans, dp[i]);
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}
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return ans;
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}
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}
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