matching brackets

matching-brackets.js

// https://www.reddit.com/r/javascript/comments/4eb61r/interview_exercise_feedback/

function isBalanced(str) {
    var dict = {
        '{': '}',
        '(': ')',
        '[': ']'
    };
    var stack = [];
    for (var i = 0; i < str.length; i++) {
        if (str[i] === dict[stack[stack.length - 1]]) {
            stack.pop();
        } else {
            stack.push(str[i]);
        }
    }
    return stack.length === 0 ? true : false;
}

let last = arr => arr[arr.length - 1];

function isBalanced2(str) {
	let dict = {
        '{': '}',
        '(': ')',
        '[': ']'
    };
    let stack = [];
	str.split('').forEach(ch => {
		if (ch === dict[last(stack)]) {
			stack.pop();
		} else {
			stack.push(ch);
		}
	});
	return stack.length === 0;
}

console.log(isBalanced2('')); // true
console.log(isBalanced2('()()')); // true
console.log(isBalanced2('{{[]()}}')); // true
console.log(isBalanced2('([)]')); // false
console.log(isBalanced2(']]')); // false
// console.log(isBalanced('((((()))))')); // true
// console.log(isBalanced('({][]})')); // false
// console.log(isBalanced('(')); // false
// console.log(isBalanced(']')); // false
// console.log('');

function isBalanced3(str) {
	const dict = {
        '{': '}',
        '(': ')',
        '[': ']'
    };
    let stack = [];
	for (let i = 0, l = str.length; i < l; i++) {
		if (str[i] === dict[last(stack)]) {
			stack.pop();
		} else if (str[i] in dict) {
			stack.push(str[i]);
		} else {
			// if we find a closing bracket and we don't have a match for it,
			// we know we have an imbalance
			return false;
		}
	}
	return stack.length === 0;
}

matching-brackets.py

def is_balanced(s):
	d = {
	    '{': '}',
	    '(': ')',
	    '[': ']'
	}
	stack = []
	for ch in s:
		if (len(stack) > 0) and (ch == d.get(stack[-1])):
			stack.pop()
		elif (ch in d):
			stack.append(ch)
		else:
			return False
	return len(stack) == 0


assert is_balanced('') # True
assert is_balanced('()()') # True
assert is_balanced('{{[]()}}') # True
assert not is_balanced('([)]') # False
assert not is_balanced(']]') # False

assert is_balanced('((((()))))') # True
assert not is_balanced('({][]})') # False
assert not is_balanced('(') # False

print('Passed!')