LeetCode-22. 括号生成-Java-medium

题目链接

法一（dfs）

public class Solution22 {

    private List<String> ans;

    public Solution22() {
        this.ans = new LinkedList<>();
    }

    /**
     * dfs
     *
     * @param left
     * @param right
     * @param curStr
     */
    private void dfs(int left, int right, String curStr) {
        if (left > right || left < 0 || right < 0) {
            return;
        }
        if (left == 0 && right == 0) {
            ans.add(curStr);
            return;
        }
        dfs(left - 1, right, curStr + "(");
        dfs(left, right - 1, curStr + ")");
    }

    /**
     * 法一（dfs）
     *
     * @param n
     * @return
     */
    public List<String> generateParenthesis(int n) {
        dfs(n, n, "");
        return ans;
    }
}
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法二（回溯）

public class Solution22 {

    private List<String> ans;

    public Solution22() {
        this.ans = new LinkedList<>();
    }
    
    /**
     * 回溯（更快）
     *
     * @param left
     * @param right
     * @param curStr
     */
    private void backtracking(int left, int right, StringBuilder curStr) {
        if (left == 0 && right == 0) {
            ans.add(curStr.toString());
            return;
        }
        if (left > 0) {
            curStr.append("(");
            backtracking(left - 1, right, curStr);
            curStr.deleteCharAt(curStr.length() - 1);
        }
        if (left < right) {
            curStr.append(")");
            backtracking(left, right - 1, curStr);
            curStr.deleteCharAt(curStr.length() - 1);
        }
    }

    /**
     * 法二（回溯）
     *
     * @param n
     * @return
     */
    public List<String> generateParenthesis_2(int n) {
        backtracking(n, n, new StringBuilder());
        return ans;
    }
}
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本地测试

        /**
         * 22. 括号生成
         */
        lay.showTitle(22);
        Solution22 sol22_1 = new Solution22();
        List<String> ans22_1 = sol22_1.generateParenthesis(3);
        arrayOpt.showStringList(ans22_1);
        Solution22 sol22_2 = new Solution22();
        List<String> ans22_2 = sol22_2.generateParenthesis_2(3);
        arrayOpt.showStringList(ans22_2);
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