383. 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

方法一：全是小写字母，可用26维数组统计各字母

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

}
};

方法二：map统计

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

}
};