316. Remove Duplicate Letters

最新推荐文章于 2022-10-17 15:38:24 发布

原创最新推荐文章于 2022-10-17 15:38:24 发布 · 691 阅读

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#greedy

本文介绍了一个算法，用于在给定只包含小写字母的字符串中去除重复字母，同时确保结果字符串按字典序是最小的。通过使用count和added数组辅助，该算法能够高效地实现这一目标。

Problem

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"

Credits:
Special thanks to @dietpepsi for adding this problem and creating all test cases

Solution

关键是要发现一个规律：从前往后扫描时，当前字符取舍在于当前结果字符串出现比它大的字符在后面的字符串是否还存在多余的，如果存在，那就把前面的删去，用后面的；否则就keep 当前的

用 count 和 added 两个数组来辅助才行。

refer https://leetcode.com/discuss/83225/clean-easy-understand-java-stack-solution-with-explanation

class Solution {
public:
    string removeDuplicateLetters(string s) {
        const int N = s.size();
        
        if( N < 2 ) return s;
        vector<int> count( 26, 0 );
        for(char c : s) {
            count[c-'a']++;
        }
        vector<bool> added(26, false);
        string rst;
        for(char c : s) {
            count[c-'a']--;
            if(added[c-'a']) continue;
            
            while(!rst.empty() && rst.back() > c && count[rst.back() -'a'] > 0) {
                added[rst.back() - 'a'] = false;
                rst.pop_back();
            }
            rst.push_back(c);
            added[c-'a'] = true;
        }
        return rst;
        
    }
};