如何删除字符串中重复的字符？

数据结构与算法

应该是要保留原数组元素的相对位置
，。，。，。选择排序类似的筛选法没问题。

1.筛选

public class Solution {
    public String removeDuplicate(String string) {
        if(string==null||string.length()==0){
            return null;
        }
        char[] chars = string.toCharArray();
        List<Character> charList = new ArrayList<>();
        for (int i = 0; i < chars.length; i++) {
            charList.add(chars[i]);
        }
        for (int i = 0; i < chars.length - 1; i++) {
            for (int j = i + 1; j < chars.length; j++) {
                if (chars[i] == chars[j]) {
                    charList.remove(j);
                }
            }
        }
        return charList.toString();
    }
    public static void main(String[] args) {
        Solution solution = new Solution();
        String string = "abac";
        System.out.println(solution.removeDuplicate(string));
    }
}

2.一次遍历

记录出现的字符

public class Solution {
    public String removeDuplicate(String string) {
        if (string == null || string.length() == 0) {
            return null;
        }
        char[] chars = string.toCharArray();
        List<Character> charList = new ArrayList<>();
        for (int i = 0; i < chars.length; i++) {
            charList.add(chars[i]);
        }
        int len = 'z' - 'A' + 1;
        boolean[] book = new boolean[len];
        int temp;
        for (int i = 0; i < chars.length; i++) {
            temp = chars[i] - 'A';
            if (book[temp] == false) {
                book[temp] = true;
            } else {
                charList.remove(i);
            }
        }
        return charList.toString();
    }
    public static void main(String[] args) {
        Solution solution = new Solution();
        String string = "abac";
        System.out.println(solution.removeDuplicate(string));
    }
}

3.不申请额外空间

，，。，就是直接置为'',.,.,.,

public class Solution {
    public String removeDuplicate(String string) {
        if (string == null || string.length() == 0) {
            return null;
        }
        char[] chars = string.toCharArray();
        int len = 'z' - 'A' + 1;
        boolean[] book = new boolean[len];
        int temp;
        for (int i = 0; i < chars.length; i++) {
            temp = chars[i] - 'A';
            if (book[temp] == false) {
                book[temp] = true;
            } else {
                chars[i] = ' ';
            }
        }
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < chars.length; i++) {
            if (chars[i] != ' ') {
                sb.append(chars[i]);
            }
        }
        return sb.toString();
    }
    public static void main(String[] args) {
        Solution solution = new Solution();
        String string = "abac";
        System.out.println(solution.removeDuplicate(string));
    }
}