Codility #7-Nesting

function solution(S) {

let stack = [];

for (let i = 0, n = S.length; i < n; i++) {

let c = S.charAt(i);

if (c === '(') {

stack.push(c);

} else if (c === ')') {

if (stack.length === 0) {

return 0;

} else if (stack[stack.length - 1] === '(') {

stack.pop();

}

}

}

return stack.length === 0 ? 1 : 0;

}