Leetcode 383 Ransom Note

Given
an
arbitrary
ransom
note
string
and
another
string
containing
lettersfrom
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:
Youmayassumethatbothstringscontainonlylowercaseletters.

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

题目大意：给两个string，判断第一个string能否由第二个string里面所含有的字母组成，
第二个string里面的所有字母只能使用一次

分析：建立一个hash数组，对第二个string遍历并记录每个字符出现的次数，然后遍历第一个string，
如果有出现hash里面不存在的字符，那么returnfalse

classSolution{
public:
boolcanConstruct(stringransomNote,stringmagazine){
inta[26]={0},lenr=ransomNote.length(),lenm=magazine.length(),i;
for(i=0;i<lenm;i++)
a[magazine[i]-'a']++;
for(i=0;i<lenr;i++)
if(a[ransomNote[i]-'a']==0)
returnfalse;
else
a[ransomNote[i]-'a']--;
returntrue;
}
};