Given a string containing only three types of characters: '(', ')' and '*', write a function to check whether this string is valid. We define the validity of a string by these rules:
- Any left parenthesis
'('
must have a corresponding right parenthesis')'
. - Any right parenthesis
')'
must have a corresponding left parenthesis'('
. - Left parenthesis
'('
must go before the corresponding right parenthesis')'
. '*'
could be treated as a single right parenthesis')'
or a single left parenthesis'('
or an empty string.- An empty string is also valid.
Example 1:
Input: "()" Output: True
Example 2:
Input: "(*)" Output: True
Example 3:
Input: "(*))" Output: True
public class Solution {
//在不存在'*'的情況下,只要用兩個計數器就可以達到要求,現在由於還有'*'
public boolean checkValidString(String s) {
return check(s,0,0,0);
}
public boolean check(String s,int k,int l,int r){
if(r>l) return false;
if(k==s.length()){
return l==r;
}
char ch=s.charAt(k);
if(ch=='*'){
if(check(s,k+1,l+1,r)) return true;
if(check(s,k+1,l,r+1)) return true;
if(check(s,k+1,l,r)) return true;
}else {
if(ch=='(') l++;
else r++;
if(check(s,k+1,l,r)) return true;
}
return false;
}
}