Problem:

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

思路：

Solution (C++):

ListNode* u;
Solution(ListNode* head) {
    u = head;
}

/** Returns a random node's value. */
bool canConstruct(string ransomNote, string magazine) {
    vector<int> vec(26, 0);
    int m = ransomNote.length(), n = magazine.length();
    for (int i = 0; i < n; ++i) {
        ++vec[magazine[i]-'a'];
    }
    for (int i = 0; i < m; ++i) {
        if (--vec[ransomNote[i]-'a'] < 0)
            return false;
    }
    return true;
}

性能：

Runtime: 20 ms  Memory Usage: 8.8 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB