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package com.baidu;import java.io.*;import java.util.*;/** * date : Dec 29, 2013 * * time : 10:07:15 AM * * author : Spole * */public class Demo04 { //要排列组合的元素个数 private static int MAX_INDEX; //当前排列中需要填入数字的索引位置 private static int finishIndex; //已经完成的排列的数量 private static int finishCount; //记录排列元素的数组 private int[] num; //当前的排列组合 private LinkedList<Integer> savedNum; public Demo04(int max) { MAX_INDEX = max; finishIndex = 0; finishCount = 0; num = new int[MAX_INDEX]; savedNum = new LinkedList<Integer>(); for(int i=0; i<MAX_INDEX; i++) { num[i] = i+1; } } public void doPermutationAndCombination() { saveNum(num); System.out.println("一共 " + finishCount + "种组合!"); } //完成排列组合,并输出到屏幕 private void saveNum(int[] num) { //循环数量由所处的递归层数决定 for(int i=0; i<MAX_INDEX-finishIndex; i++) { //添加选中的元素到链表 savedNum.addLast(num[i]); //记录已经选取的元素 int numBuf = num[i]; //记录以完成的排列组合数量 if(finishIndex == (MAX_INDEX-1)) { finishCount++; } //创建传入递归下一层要用的数组 int nextNum[] = new int[MAX_INDEX - (finishIndex+1)]; int m = 0; //拷贝未选用的数字 for(int n=0; n<MAX_INDEX-finishIndex; n++) { if(num[n] == numBuf) { continue; } else { nextNum[m] = num[n]; m++; } } //是否继续递归 if((MAX_INDEX - (finishIndex+1)) != 0) { //递归层数计数加1 finishIndex++; saveNum(nextNum); } else { //输出这一轮递归生成的数字组合 System.out.println(savedNum); } } try { //判断是否是递归的最后一层 if(finishIndex == (MAX_INDEX-1)) { //移除排列组合的最后一位元素 savedNum.removeLast(); //移除排列组合的最后一位元素 savedNum.removeLast(); } else { //移除排列组合的最后一位元素 savedNum.removeLast(); } } catch(Exception e){} finally { //回到上一层,递归层数要减1 finishIndex--; } } public static void main(String[] args) { String theMaxString = null; int theMax = 0; try { System.out.print("请输入数字: "); BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); theMaxString = br.readLine().trim(); } catch(Exception e) { e.printStackTrace(); } try { theMax = Integer.parseInt(theMaxString); } catch(Exception e) { System.out.println("输入的数字格式不正确!"); } Demo04 p = new Demo04(theMax); Date date = new Date(); p.doPermutationAndCombination(); System.out.println("用时" + (new Date().getTime() - date.getTime()) + "毫秒"); }}
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