***Leetcode 767. Reorganize String

Posted 2022-12-03 Z-Pilgrim

https://leetcode.com/problems/reorganize-string/description/

套路题了

如果是判断是否可行，判断条件就是最多的不能超过总长度的一半（考虑计数情况）

如果是找方案 就需要优先队列了。。

 

struct cmp 
    bool operator()(const pair<int, int> & a, const pair<int, int>&b) 
        if (a.second != b.second ) return a.second < b.second;
        return a.first < b.first;
    
;


class Solution 
public:
    string reorganizeString(string s) 
        vector< pair<char, int> >  mem( 256, make_pair('\\0', 0) ) ;
        
        for (int i = 0; i < mem.size(); i++) 
            mem[i].first = (char)i;
        for (auto c:s) mem[c].second ++;
        
        
        priority_queue< pair<int, int>, vector< pair<int, int> >, cmp > q;
        for (int i = 0; i < 256; i++) 
            if (mem[i].second >  (s.size() + 1)/2 ) return "";
            if (mem[i].second) 
                q.push( mem[i] );
            
        
        
        string ret;
        for (int i = 0; i < s.size(); i++) 
                pair<int, int> one = q.top(); q.pop();
                if ( ret.empty() || ret.back() != one.first  ) 
                    ret += one.first;
                    one.second--;
                    q.push(one);
                 else 
                    if (q.empty()) return "";
                    pair<int, int> two = q.top(); q.pop();
                    if (ret.back() != two.first) 
                        ret += two.first;
                        two.second --;
                     else 
                        return "";
                    
                    
                    if (two.second)
                        q.push(two);
                    if (one.second)
                        q.push(one);
                
        

        return ret.size() == s.size() ? ret : "";
    
;