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();
   }
 }