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

class Solution {
public:
bool canConstruct(string ransomNote, string magazine) {
const int len1 = ransomNote.length();
const int len2 = magazine.length();
if(len1 == 0 && len2 == 0)
return true;

unordered_map<int, int> umap;
for(int i=0; i<len1; ++i)
umap[ransomNote[i]]++;
for(int i=0; i<len2; ++i)
umap[magazine[i]]--;
auto it = find_if(umap.begin(), umap.end(), [](const pair<int, int>& pr)
{return pr.second > 0;} );
return it == umap.end();
}
};

class Solution {
public:
bool canConstruct(string ransomNote, string magazine) {
const int len1 = ransomNote.length();
const int len2 = magazine.length();
if(len1 == 0 && len2 == 0)
return true;

unordered_map<int, int> umap;
for(int i=0; i<len2; ++i)
umap[magazine[i]]++;
for(int i=0; i<len1; ++i) {
if(--umap[ransomNote[i]] < 0)
return false;
}
return true;
}
};