383. Ransom Note【easy】

383. Ransom Note【easy】

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

解法一：

class Solution {
public:
    bool canConstruct(string ransomNote, string magazine) {
        map<char, int> m_rans;
        
        for (int i = 0; i < ransomNote.length(); ++i) {
            ++m_rans[ransomNote[i]];
        }
        
        for (int i = 0; i < magazine.length(); ++i) {
            if (m_rans.find(magazine[i]) != m_rans.end()) {
                --m_rans[magazine[i]];
            }
        }
        
        for (map<char, int>::iterator it = m_rans.begin(); it != m_rans.end(); ++it) {
            if (it->second > 0) {
                return false;
            }
        }
        
        return true;
    }
};

解法二：

public class Solution {
    public boolean canConstruct(String ransomNote, String magazine) {
        int[] arr = new int[26];
        for (int i = 0; i < magazine.length(); i++) {
            arr[magazine.charAt(i) - 'a']++;
        }
        for (int i = 0; i < ransomNote.length(); i++) {
            if(--arr[ransomNote.charAt(i)-'a'] < 0) {
                return false;
            }
        }
        return true;
    }
}

参考@yidongwang 的代码。

解法三：

class Solution {
public:
    bool canConstruct(string ransomNote, string magazine) {
        unordered_map<char, int> map(26);
        for (int i = 0; i < magazine.size(); ++i)
            ++map[magazine[i]];
        for (int j = 0; j < ransomNote.size(); ++j)
            if (--map[ransomNote[j]] < 0)
                return false;
        return true;
    }
};

参考@haruhiku 的代码

解法四：

class Solution {
public:
    bool canConstruct(string ransomNote, string magazine) {
        vector<int> vec(26, 0);
        for (int i = 0; i < magazine.size(); ++i)
            ++vec[magazine[i] - 'a'];
        for (int j = 0; j < ransomNote.size(); ++j)
            if (--vec[ransomNote[j] - 'a'] < 0)
                return false;
        return true;
    }
};

参考@haruhiku 的代码