22. 括号生成

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);
    }
}