[백준/Java] 15649 N과 M(1)

문제

https://www.acmicpc.net/problem/15649

풀이방법

StringBuilder를 사용하면 시간이 정말 많이 줄어든다~~~

풀이

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main{
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());
        int N = Integer.parseInt(st.nextToken());
        int M = Integer.parseInt(st.nextToken());
        int[] result = new int[M];

        backtracking(N, M, 0, 0, result);
    }
    static void backtracking(int N, int M,  int depth, int bitmask, int[] result) {
        if (depth == M) {
            for(int i = 0; i<M; i++) {
                System.out.print(result[i] + " ");
            }
            System.out.println();
            return;
        }
        for (int i = 1; i<=N; i++) {
            if ((bitmask & (1<<i))==0) {
                result[depth] = i;
                backtracking(N, M, depth + 1,bitmask| 1<<i, result);
            }
        }
    }
}

 

StringBuilder

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());

        int N = Integer.parseInt(st.nextToken());
        int M = Integer.parseInt(st.nextToken());

        int[] result = new int[M];
        StringBuilder sb = new StringBuilder();

        backtracking(N, M, 0, 0, result, sb);
        System.out.print(sb);
    }
    static void backtracking(int N, int M, int depth, int bitmask, int[] result, StringBuilder sb) {
        if (depth == M) {
            for (int i = 0; i < M; i++) {
                sb.append(result[i]).append(" ");
            }
            sb.append('\n');
            return;
        }

        for (int i = 1; i <= N; i++) {
            if ((bitmask & (1 << i)) == 0) {
                result[depth] = i;
                backtracking(N, M, depth + 1, bitmask | (1 << i), result, sb);
            }
        }
    }
}