383. Ransom Note

原題網址：https://leetcode.com/problems/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：直方圖頻率統計。

public class Solution {
    private int[] frequency(String s) {
        int[] f = new int[26];
        char[] sa = s.toCharArray();
        for(char c : sa) {
            f[c - 'a'] ++;
        }
        return f;
    }
    public boolean canConstruct(String ransomNote, String magazine) {
        int[] fr = frequency(ransomNote);
        int[] fm = frequency(magazine);
        for(int i = 0; i < fr.length; i++) {
            if (fr[i] > fm[i]) {
                return false;
            }
        }
        return true;
    }
}