Leetcode 767. Refactored strings

Leetcode 767. Refactored strings

Question stem

Given a string S, check whether the letters can be rearranged so that two adjacent characters are different.
If feasible, output any feasible results. If not feasible, return an empty string.

Example 1:
Input: S = "aab"
Output: "aba"

Example 2:
Input: S = "aaab"
Output: ""

Note:
S only contains lowercase letters and the length is in the interval [1, 500].

answer

Count the number of occurrences of letters, sort them in descending order according to the number of times, and then put the letters back to S in the order of odd first (index=0) and then even

class Solution {
    
    
public:
    string reorganizeString(string S) {
    
    
        int n = S.length();
        int head = 0,tail = n-1;
        vector<string> alphaCount(26,"");
        if(n==0){
    
    
            return "";
        }else if(n==1){
    
    
            return S;
        }
        for(int i = 0 ; i < n ; ++i){
    
    
            alphaCount[S[i] - 'a'].push_back(S[i]);
        }   
        //字符串长度即字符出现次数，按照字符出现次数降序排列
        sort(alphaCount.begin(),alphaCount.end(),[&](string a,string b){
    
    
            return a.length() > b.length();
        });
        if(alphaCount[0].length() > (n + 1) / 2){
    
    
            return "";
        }
        //按照奇偶填充
        int ptr = 0;
        int evenPtr = 1;
        int oddPtr = 0;
        for(int i = 0;i<26;++i){
    
    
            while(!alphaCount[i].empty() && oddPtr < n){
    
    
                S[oddPtr] = alphaCount[i].back();
                alphaCount[i].pop_back();
                oddPtr += 2;
            }
            while(!alphaCount[i].empty()){
    
    
                S[evenPtr] = alphaCount[i].back();
                alphaCount[i].pop_back();
                evenPtr += 2;
            }
        }
        return S;
    }
};