[Codility] Stacks and Queues - Brackets / Java

1. 문제

A string S consisting of N characters is considered to be properly nested if any of the following conditions is true:

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

For example, the string "{[()()]}" is properly nested but "([)()]" is not.

Write a function:

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

that, given a string S consisting of N characters, returns 1 if 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..200,000];
• string S consists only of the following characters: "(", "{", "[", "]", "}" and/or ")".

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2. 코드

import java.util.*;

class Solution {
    public int solution(String S) {
  
        Stack<Character> stack = new Stack<>();
  
        for(int i=0; i<S.length(); i++) {
            char c = S.charAt(i);
            if(c == '(' || c == '[' || c == '{')
                stack.push(c);
            else {
                if(stack.empty())
                    return 0;
                    
                Character item = stack.peek();
                stack.pop();
                
                if(item == '{' && c != '}')
                    return 0;
                else if(item == '[' && c != ']')
                    return 0;
                else if(item == '(' && c != ')')
                    return 0;
                
            }
        }
        
        if(stack.empty())
            return 1;
        else
            return 0;
    }
}