CCI 9.5 字符串全排列

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编写一个方法，确定某字符串的所有排列组合。

package cci;import java.util.ArrayList;public class CCI_9_5 {public static ArrayList<String> permutation(String str){if(str==null)return null;ArrayList<String> result = new ArrayList<String>();if(str.length()<=1){result.add(str);return result;}char first = str.charAt(0);String sub = str.substring(1);ArrayList<String> perms = permutation(sub);for(String perm : perms){for(int i=0; i<=perm.length(); i++){String temp = insertCharAt(perm, i, first);result.add(temp);}}return result;}private static String insertCharAt(String str, int index, char c){String pre = str.substring(0,index);String post = str.substring(index);return pre+c+post;}public static void main(String[] args) {// TODO Auto-generated method stubString str = "abc";ArrayList<String> result = permutation(str);for(String item : result){System.out.println(item);}}}

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