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package class28;
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import java.util.ArrayList;
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import java.util.List;
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public class Problem_0022_GenerateParentheses {
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public static List<String> generateParenthesis(int n) {
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char[] path = new char[n << 1];
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List<String> ans = new ArrayList<>();
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process(path, 0, 0, n, ans);
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return ans;
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}
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// path 做的决定 path[0....index-1]做完决定的！
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// path[index.....] 还没做决定，当前轮到index位置做决定！
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public static void process(char[] path, int index, int leftMinusRight, int leftRest, List<String> ans) {
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if (index == path.length) {
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ans.add(String.valueOf(path));
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} else {
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// index ( )
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if (leftRest > 0) {
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path[index] = '(';
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process(path, index + 1, leftMinusRight + 1, leftRest - 1, ans);
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}
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if (leftMinusRight > 0) {
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path[index] = ')';
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process(path, index + 1, leftMinusRight - 1, leftRest, ans);
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}
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}
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}
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// 不剪枝的做法
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public static List<String> generateParenthesis2(int n) {
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char[] path = new char[n << 1];
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List<String> ans = new ArrayList<>();
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process2(path, 0, ans);
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return ans;
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}
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public static void process2(char[] path, int index, List<String> ans) {
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if (index == path.length) {
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if (isValid(path)) {
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ans.add(String.valueOf(path));
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}
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} else {
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path[index] = '(';
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process2(path, index + 1, ans);
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path[index] = ')';
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process2(path, index + 1, ans);
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}
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}
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public static boolean isValid(char[] path) {
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int count = 0;
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for (char cha : path) {
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if (cha == '(') {
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count++;
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} else {
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count--;
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}
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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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}
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