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Permutation2.java
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68 lines (58 loc) · 1.86 KB
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package org.study;
import java.util.*;
/**
* 순열 : n 개 중에서 r 개 선택
* 시간복잡도는 O(n!)
* 연습문제 : https://www.acmicpc.net/problem/10974
*/
public class Permutation2 {
public static void main(String[] args) {
int n = 3;
int[] arr = {1, 2, 3};
int[] output = new int[n];
boolean[] visited = new boolean[n];
perm(arr, output, visited, 0, n, 3);
System.out.println();
permutation(arr, 0, n, 3);
}
// 순서를 지키면서 n 개중에서 r 개를 뽑는 경우
// 사용 예시: perm(arr, output, visited, 0, n, 3);
static void perm(int[] arr, int[] output, boolean[] visited, int depth, int n, int r) {
if(depth == r) {
print(output, r);
return;
}
for(int i=0; i<n; i++) {
if(visited[i] != true) {
visited[i] = true;
output[depth] = arr[i];
perm(arr, output, visited, depth + 1, n, r);
visited[i] = false;
}
}
}
// 순서 없이 n 개중에서 r 개를 뽑는 경우
// 사용 예시: permutation(arr, 0, n, 4);
static void permutation(int[] arr, int depth, int n, int r) {
if(depth == r) {
print(arr, r);
return;
}
for(int i=depth; i<n; i++) {
swap(arr, depth, i);
permutation(arr, depth + 1, n, r);
swap(arr, depth, i);
}
}
static void swap(int[] arr, int depth, int i) {
int temp = arr[depth];
arr[depth] = arr[i];
arr[i] = temp;
}
// 배열 출력
static void print(int[] arr, int r) {
for(int i=0; i<r; i++)
System.out.print(arr[i] + " ");
System.out.println();
}
}