22. 括号生成

回溯

class Solution {List<String> res = new ArrayList<>();StringBuilder path = new StringBuilder();  // path推荐这种写法public List<String> generateParenthesis(int n) {backtrack(n, 0, 0);return res;}void backtrack(int n, int l, int r){if(r > l || l > n || r > n) return;if(l == n && r == n){res.add(path.toString());return;}path.append('(');backtrack(n, l + 1, r);path.deleteCharAt(path.length() - 1);path.append(')');backtrack(n, l, r + 1);path.deleteCharAt(path.length() - 1);}
}