Ransom Note

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.

1 2 3

canConstruct("a", "b") -> false canConstruct("aa", "ab") -> false canConstruct("aa", "aab") -> true

Original url：leetcode Ransom Note

Analysis:

This is to count the number of characters in magazine and characters in ransom note. use haspmap or array. since note contains only lowercase letters, array is enought.

This is also a method to tell if a set is a subset of another set.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

public class Solution { public boolean canConstruct(String ransomNote, String magazine) { int[] cnt = new int[26]; //collect statistics of characters in magzine for (int i = 0; i < magazine.length(); i++){ cnt[magazine.charAt(i) - 97]++; } //consume the statistics by examing the ransom note for (int i = 0; i < ransomNote.length(); i++){ if (--cnt[ransomNote.charAt(i) - 97] < 0){ return false; } } return true; } }