题目讲解

1419. 数青蛙

算法讲解

class Solution {
public:
    int minNumberOfFrogs(string croakOfFrogs) {
        string target = "croak";
        int n = target.size();

        //保存target每个字符的位置index
        unordered_map<char, int>index;
        for(int i = 0; i < n; i++)index[target[i]] = i;

        //按照target的顺序制作Hash
        vector<int>Hash(n); 

        for(int i = 0; i < croakOfFrogs.size(); i++)
        {
            if(croakOfFrogs[i] == 'c')
            {
                if(Hash[n-1] != 0)Hash[n-1]--;
                Hash[0]++;
            }
            else
            {
                //获取当前 croak 字母的下标
                int char_index = index[croakOfFrogs[i]];
                //判断前一个字符是否在Hash中出现 
                if(Hash[char_index - 1] == 0)return -1;
                Hash[char_index - 1]--; Hash[char_index]++;
            }

           
        }
         //怕出现这种croakcro
        for(int i = 0; i < n-1; i++)
        {
            if(Hash[i] != 0)return -1;
        }
        return Hash[n-1];
    }
};