1234 1243 1324 1342 1423 1432 2134 2143 2314 2341 2413 2431 3124 3142 3214 3241 3412 3421 4123 4132 4213 4231 4312 43211123 1132 1213 1231 1312 1321 2113 2131 2311 3112 3121 32111023 1032 1203 1230 1302 1320 2013 2031 2103 2130 2301 2310 3012 3021 3102 3120 3201 3210

题意：给出4张卡片，第张卡片上的数为o-9之间，求构成的4位数的所有排列（当然不能有前导0）

思路：第一种直接使用STL中的next_permutation算法，第二种使用字典序生成排列算法

字典序生成排列算法思想

（1）假设当前序列为a1a2a3...an，从后往前找到ai<ai+1,记录下当前的i,

(2)从右到左找到aj>ai,替换ai和aj，然后将从i+1 到最后公位置从小到大排列

（3）直接找不到满足条件的i为止

第一种解法代码如下

#include <cstdio>
#include <algorithm>using namespace std;const int N = 4;int a[N];
int cs = 0;bool input()
{int sum = 0;for (int i = 0; i < N; i++) {scanf("%d", &a[i]);sum += a[i];}if (sum == 0) return false;return true;
}void solve()
{if (cs) printf("\n");cs++;sort(a, a + N);bool flag = true;int prev = -1;do {if (a[0] == 0) continue;//表示第一行的第一个if (flag) {flag = false;for (int i = 0; i < N; i++) {printf("%d", a[i]);}} else if (a[0] == prev) {printf(" ");for (int i = 0; i < N; i++) {printf("%d", a[i]);}} else {printf("\n");for (int i = 0; i < N; i++) {printf("%d", a[i]);}}prev = a[0];} while (next_permutation(a, a + N));printf("\n");
}int main()
{
#ifndef ONLINE_JUDGEfreopen("f:\\OJ\\uva_in.txt", "r", stdin);
#endifwhile (input()) {solve();}return 0;
}

第二种解法（字典序生成法）代码如下

import java.io.FileInputStream;
import java.io.OutputStreamWriter;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Scanner;
import java.util.Arrays;public class Main implements Runnable
{  private static final boolean DEBUG = false;private Scanner cin;private PrintWriter cout;private static final int N = 4;private static final int[] a = new int[N];private int cs = 0;private void init(){try {if (DEBUG) {cin = new Scanner(new InputStreamReader(new FileInputStream("f:\\OJ\\uva_in.txt")));} else {cin = new Scanner(new InputStreamReader(System.in));}cout = new PrintWriter(new OutputStreamWriter(System.out));} catch (Exception e) {e.printStackTrace();}  }private boolean input(){int sum = 0;for (int i = 0; i < N; i++) {a[i] = cin.nextInt();sum += a[i];}if (sum == 0) return false;return true;}private boolean next_permutation(int[] array){int len = array.length;int i = len - 1, j;while (true) {j = i;i--;if (array[i] < array[j]) {int k = len - 1;while (!(array[i] < array[k])) k--;int tmp = array[i];array[i] = array[k];array[k] = tmp;Arrays.sort(array, j, len);return true;}if (i == 0) {Arrays.sort(array);return false;}}}private void solve(){if (cs != 0) cout.println();cs++;Arrays.sort(a);boolean flag = true;int prev = 0;do {if (a[0] == 0) continue;if (flag) {flag = false;for (int i = 0; i < N; i++) {cout.print(a[i]);}} else if (a[0] == prev) {cout.print(" ");for (int i = 0; i < N; i++) {cout.print(a[i]);}} else {cout.println();for (int i = 0; i < N; i++) {cout.print(a[i]);}}prev = a[0];} while (next_permutation(a));cout.println();cout.flush();}@Overridepublic void run(){init();while (input()) {solve();}}public static void main(String[] args) {// TODO code application logic herenew Thread(new Main()).start();}
}