1~n的全排列--阅文集团2018校招笔试题

题目大意：给定整数n，求出1~n的全排列

示例

输入：n=3

输出：[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]

import java.util.Scanner;
import java.util.ArrayList;

public class Main{
  private void func(ArrayList<Integer> nArray, ArrayList<ArrayList<Integer>> results, ArrayList<Integer> oneResult) {
    int nArraySize = nArray.size();
    if(nArraySize == 0) {
      results.add(new ArrayList<Integer>(oneResult)); // 要新建一个类加入到结果集中，不然最终结果集中所有结果都一样（因为是同一个ArrayList）      
      return;
    }
    int tmp = 0;
    for(int i=0; i<nArraySize; i++) {
      tmp = nArray.get(i);
      nArray.remove(i);
      oneResult.add(tmp);
      func(nArray, results, oneResult);
      nArray.add(i, tmp);
      oneResult.remove(oneResult.size()-1);
    }
    
  }
  
  public static void main(String[] args) {
    Main mainClass = new Main();
    Scanner in = new Scanner(System.in);
    while(in.hasNext()) {
      String input = in.next();
      int n = Integer.parseInt(input.split("=")[1]);
      ArrayList<Integer> nArray = new ArrayList<Integer>();
      for(int i=1; i<=n; i++) {
        nArray.add(i);
      }
      
      ArrayList<ArrayList<Integer>> results = new ArrayList<ArrayList<Integer>>();
      mainClass.func(nArray, results, new ArrayList<Integer>());
      
      /**
       * 构造输出格式
       */
      StringBuilder stringBuilder = new StringBuilder();
      for(int i=0; i<results.size(); i++) {
        if(i > 0) {
              stringBuilder.append(",");
          }
        stringBuilder.append("[");
        for(int j=0; j<results.get(i).size(); j++) {
          if(j > 0) {
              stringBuilder.append(",");
          }
          stringBuilder.append(results.get(i).get(j));
        }
        stringBuilder.append("]");
      }
      
      System.out.println(stringBuilder.toString());
    }
    in.close();
  }
}