LeetCode-383. Ransom Note

Description

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

Solution 1(C++)

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

Solution 2(C++)

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;
}
};

算法分析

程序分析