LeetCode 316. Remove Duplicate Letters--贪心算法

题目链接

316. Remove Duplicate Letters

Given a string which contains only lowercase letters, remove duplicate letters so that every letter appear once and only once. You must make sure your result is the smallest in lexicographical order among all possible results.

Example:

Given "bcabc"
Return "abc"

Given "cbacdcbc"
Return "acdb"

解：在每次循环中：

1.计算一个end[26]数组值，代表每个字母在s中最后出现的位置

2.从0开始++，找到一个位置是某个字母最后出现的位置j

3.在0～j位置中找到字典序最大的字母，将这个字母加到结果字符串中，将其前面位置的字符和后面字符串中的这个字母全部删掉，变成一个新的s

s为空时跳出循环

代码：

class Solution {public:    string removeDuplicateLetters(string s) {        string result = "";        while (s != "") {            int end[26] = {};            int len = s.length();            for (int i = 0; i < len; i++) end[s[i]-'a'] = i;            int j = 0;            int pos = 0;            char smallest = 'z';            for (j = 0; j < len; j++) {                if (s[j] < smallest) {                    pos = j;                    smallest = s[j];                }                if (end[s[j]-'a'] == j) break;            }            result += smallest;            s = s.substr(pos+1, len-1-pos);            string::iterator it;            for (it =s.begin(); it != s.end();)                if(*it == smallest) it = s.erase(it);                else ++it;        }        return result;    }};