出鞘之剑指offer-第38题 (字符串的排列)

题目：

输入一个字符串，打印出该字符串中字符的所有排列。 

分析一：

用递归

代码一：

package offer.xzs.thirty2thirtynine.thirtyeight;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Demo01 {

    public static List<String> result = new ArrayList<>();
    public static void main(String[] args) {
        String str = "abc";
        List<String> str1 = getStr(str);
        for (int i = 0; i < str1.size(); i++) {
            System.out.println(str1.get(i));
        }
    }
    public static List<String> getStr(String str) {
        if (str.length() == 0) {
            return result;
        }
        StringBuilder sb = new StringBuilder();
        char[] chars = str.toCharArray();
        boolean[] cf = new boolean[chars.length];
        Arrays.sort(chars);
        traceback(chars, cf, sb);
        return result;
    }

    private static void traceback(char[] chars, boolean[] cf, StringBuilder sb) {
        if (chars.length == sb.length()) {
            result.add(sb.toString());
            return;
        }
        for (int i = 0; i < chars.length; i++) {
            if (cf[i]) {
                continue;
            }
            if (i != 0 && chars[i] == chars[i - 1] && !cf[i - 1]) {
                continue;
            }
            cf[i] = true;
            sb.append(chars[i]);
            traceback(chars, cf, sb);
            sb.deleteCharAt(sb.length() - 1);
            cf[i] = false;
        }
    }
}

代码二：

package offer.xzs.thirty2thirtynine.thirtyeight;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Demo02 {
    public static void main(String[] args) {
        String str = "abc";
        List<String> str1 = getStr(str);
        for (int i = 0; i < str1.size(); i++) {
            System.out.println(str1.get(i));
        }
    }

    public static List<String> getStr(String str) {
        List<String> result = new ArrayList<>();
        if (str.length() == 0 || str == null) {
            return result;
        }
        char[] chars = str.toCharArray();
        traceback(result, chars, 0);
        Collections.sort(result);
        return result;
    }

    private static void traceback(List<String> result, char[] chars, int start) {
        if (start == chars.length - 1) {
            String str = String.valueOf(chars);
            if (!result.contains(str)) {
                result.add(str);
            }
        }
        for (int i = start; i < chars.length; i++) {
            char temp = chars[start];
            chars[start] = chars[i];
            chars[i] = temp;

            traceback(result, chars, start + 1);

            temp = chars[start];
            chars[start] = chars[i];
            chars[i] = temp;
        }
    }


}