LeetCode : Ransom Note

Given an arbitrary ransom note string and another string containing letters from all the magazines, write a function that will return true if the ransom note can be constructed from the magazines ; otherwise, it will return false.

Each letter in the magazine string can only be used once in your ransom note.

Note:
You may assume that both strings contain only lowercase letters.

canConstruct(“a”, “b”) -> false
canConstruct(“aa”, “ab”) -> false
canConstruct(“aa”, “aab”) -> true

class Solution {public:    bool canConstruct(string ransomNote, string magazine) {     int countM[256] = {0};     int countR[256] = {0};     if(ransomNote.size()>magazine.size())           return false;        for(int i=0;i<magazine.length();++i)        {             countM[magazine[i]]++;        }        for(int k = 0;k<ransomNote.length();++k)        {            countR[ransomNote[k]]++;        }        for(int j = 0;j<256;++j)        {           if(countM[j]<countR[j])               return false;        }        return true;    }};