字符串的排列组合(组合需无重复字母)

import java.util.Arrays;import java.util.Iterator;import java.util.Scanner;import java.util.Stack;//字符串的排列组合public class Combination {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubScanner scan = new Scanner(System.in);String string = scan.next();Stack<Character> result = new Stack<Character>();System.out.println("字符串的全部组合方法0");Allcombine(string, result);System.out.println("字符串的全部组合方法1");for (int i = 1; i <= string.length(); i++) {Allcombineone(string, i, result);// 字符串的全部组合}System.out.println("字符串的全部组合方法2");Allcombinetwo(string);System.out.println("字符串的全部排列");permutation(string.toCharArray(), 0);char[] a = new char[5];Arrays.fill(a, 'a');System.out.println(a);}public static void Allcombine(String string, Stack<Character> result) {if (string.length() == 0) {Iterator<Character> it = result.iterator();while (it.hasNext()) {System.out.print(it.next());}System.out.println();return;}// if (string.length() == 0 || string == null) {// return;// }result.push(string.charAt(0));Allcombine(string.substring(1, string.length()), result);result.pop();//System.out.println("字符串长度" + string.length());Allcombine(string.substring(1, string.length()), result);}public static void Allcombineone(String string, int number,Stack<Character> result) {if (number == 0) {Iterator<Character> it = result.iterator();while (it.hasNext()) {System.out.print(it.next());}System.out.println();return;}if (string.length() == 0 || string == null) {return;}result.push(string.charAt(0));Allcombineone(string.substring(1, string.length()), number - 1, result);result.pop();Allcombineone(string.substring(1, string.length()), number, result);}// 将1到N-1用二进制表示，有1的输出该位置的字母，方法非常好，主要用到移位操作public static void Allcombinetwo(String str) {int N = str.length();int num = (int) Math.pow(2.0, N);// Cn0+Cn1+Cn2+......+Cnn=2的n次方for (int i = 1; i < num; i++) {for (int j = 0; j < N; j++) {if (((i >> j) & 1) != 0)System.out.print(str.charAt(j));}System.out.println();}}// 全排列public static void permutation(char[] str, int start) {if (str == null || str.length == 0) {return;}if (start == str.length) {System.out.println(str);return;}for (int i = start; i < str.length; i++) {if (isExist(str, start, i)) {//加上这个条件变成有重复字母下的全排列char temp1 = str[i];str[i] = str[start];str[start] = temp1;permutation(str, start + 1);char temp2 = str[i];str[i] = str[start];str[start] = temp2;}}}//判断str[i]在(start到i-1)的范围内是否出现过public static boolean isExist(char[] str , int start , int i){for(int j =start;j<i;j++ ){if(str[j]==str[i])return false;}return true;}}