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#yyds干货盘点# LeetCode 热题 HOT 100：括号生成
source link: https://blog.51cto.com/u_13321676/5691617
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#yyds干货盘点# LeetCode 热题 HOT 100：括号生成
精选 原创数字 n 代表生成括号的对数，请你设计一个函数，用于能够生成所有可能的并且 有效的 括号组合。
输入：n = 3
输出：["((()))","(()())","(())()","()(())","()()()"]
输入：n = 1
输出：["()"]
代码实现：
class Solution {
public List<String> generateParenthesis(int n) {
List<String> ans = new ArrayList<String>();
backtrack(ans, new StringBuilder(), 0, 0, n);
return ans;
}
public void backtrack(List<String> ans, StringBuilder cur, int open, int close, int max) {
if (cur.length() == max * 2) {
ans.add(cur.toString());
return;
}
if (open < max) {
cur.append('(');
backtrack(ans, cur, open + 1, close, max);
cur.deleteCharAt(cur.length() - 1);
}
if (close < open) {
cur.append(')');
backtrack(ans, cur, open, close + 1, max);
cur.deleteCharAt(cur.length() - 1);
}
}
}
public List<String> generateParenthesis(int n) {
List<String> ans = new ArrayList<String>();
backtrack(ans, new StringBuilder(), 0, 0, n);
return ans;
}
public void backtrack(List<String> ans, StringBuilder cur, int open, int close, int max) {
if (cur.length() == max * 2) {
ans.add(cur.toString());
return;
}
if (open < max) {
cur.append('(');
backtrack(ans, cur, open + 1, close, max);
cur.deleteCharAt(cur.length() - 1);
}
if (close < open) {
cur.append(')');
backtrack(ans, cur, open, close + 1, max);
cur.deleteCharAt(cur.length() - 1);
}
}
}
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