Codility 20번 Nesting

Nesting

 

A string S consisting of N characters is called properly nested if:

• S is empty;
• S has the form "(U)" where U is a properly nested string;
• S has the form "VW" where V and W are properly nested strings.

For example, string "(()(())())" is properly nested but string "())" isn't.

Write a function:

class Solution { public int solution(String S); }

that, given a string S consisting of N characters, returns 1 if string S is properly nested and 0 otherwise.

For example, given S = "(()(())())", the function should return 1 and given S = "())", the function should return 0, as explained above.

Write an efficient algorithm for the following assumptions:

• N is an integer within the range [0..1,000,000];
• string S consists only of the characters "(" and/or ")".

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import java.util.Stack;

class Solution {
    public int solution(String S) {
        Stack<Character> sstack = new Stack<Character>();
        
        if(S.equals("")){
            return 1;
        }

        for(int i=0; i<S.length();i++){
            if(S.charAt(i)==')'){
                if(sstack.empty()){
                    return 0;
                }
                if(sstack.pop() != '('){
                    return 0;
                }
            }else{
                sstack.push(S.charAt(i));
            }
        }
        if(!sstack.empty()){
            return 0;
        }
        return 1;
    }
}

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