[Leetcode] 383. Ransom Note 解题报告

题目：

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：

Easy级别的题目。一种做法是建立哈希表，但是由于题目限定了string中只包含小写字母，所以我们用一个定长数组来实现，效率更高。

代码：

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