383. Ransom Note

1. 问题描述

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

Tags: String

2. 解题思路

3. 代码

class Solution {
public:
    bool canConstruct(string ransomNote, string magazine)
    {
        std::map<char, int> m1;
        for (int i=0; i<magazine.size(); i++)
        {
            m1[magazine[i]]++;
        }

        std::map<char, int> m2;
        for (int i=0; i<ransomNote.size(); i++)
        {
            m2[ransomNote[i]]++;
        }

        if (m2.size() > m1.size())
        {
            return false;
        }

        map<char, int>::iterator it = m2.begin();
        map<char, int>::iterator itEnd = m2.end();
        for (; it != itEnd; it++)
        {
            if (m1.count(it->first) == 0)
            {
                return false;
            }

            if (it->second > m1[it->first])
            {
                return false;
            }
        }
        return true;
    }
};

4. 反思