9.5---所有字符串的排列组合（CC150）

1，这个是自己写的。一直LTE。

    public static ArrayList<String> getPerms(String str) {
        if (str == null) {
            return null;
        }
        ArrayList<String> permutations = new ArrayList<String>();
        if (str.length() == 0) { // base case
            permutations.add("");
            return permutations;
        }
                
        char first = str.charAt(0); // get the first character
        String remainder = str.substring(1); // remove the first character
        ArrayList<String> words = getPerms(remainder);
        for (String word : words) {
            for (int j = 0; j <= word.length(); j++) {
                String s = insertCharAt(word, first, j);
                permutations.add(s);
            }
        }
        return permutations;
    }
    
    public static String insertCharAt(String word, char c, int i) {
        String start = word.substring(0, i);
        String end = word.substring(i);
        return start + c + end;
    }
    
    public static ArrayList<String> getPermutation(String str) {
        ArrayList<String> permutations = getPerms(str);
        
        ArrayList<String> res3 = new ArrayList();
        String max = new String();
    
        int flag = 0;
        int h = permutations.size();
        int sum = 0;
        while(res3.size() != h){
            max=permutations.get(0);
            for(int i = 0; i < permutations.size(); i++){
                
                if(max.compareTo(permutations.get(i))<0){
                    max = permutations.get(i);
                    flag = i;
                }
            }
            
            res3.add(new String(max));
            permutations.remove(flag);
            flag = 0;
            sum = 0;
        }
        return res3;
    }

2，这是别人写的。

下次再看吧。