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added solution for MinStack #1

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82 changes: 58 additions & 24 deletions data-structures/stack.js
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Original file line number Diff line number Diff line change
Expand Up @@ -56,30 +56,6 @@ Implement k stacks in a single array of fixed length. Start by first implementin

Balanced parens.

function balanced (str) {
return Array.prototype.reduce.call(str, function(acc, el){
if (el === '(') {
return {
left: acc.left + 1,
right: acc.right,
valid: acc.valid
}
} else if (el === ')') {
return {
left: acc.left,
right: acc.right + 1,
valid: ((acc.left <= acc.right + 1) && acc.valid)
}
} else {
return acc
}
}, {
left: 0,
right: 0,
valid: true
})
}

*/

function Stack(capacity) {
Expand Down Expand Up @@ -127,3 +103,61 @@ console.log(myStack.pop(), 'should be c');
console.log(myStack.count(), 'should be 2');
console.log(myStack.peek(), 'should be b');
console.log(myStack.count(), 'should be 2');

function MinStack(capacity) {
this._capacity = capacity;
this._storage = {};
this._count = 0;
this._min = new Stack(capacity);
}

// O(1)
MinStack.prototype.push = function(value) {
if (this._count < this._capacity) {
if (this._min.peek() < value) {
this._min.push(this._min.peek());
} else {
this._min.push(value);
}
this._storage[this._count++] = value;
return this._count;
}
return 'Max capacity already reached. Remove element before adding a new one.';
};

// O(1)
MinStack.prototype.pop = function() {
this._min.pop();
var value = this._storage[--this._count];
delete this._storage[this._count];
if (this._count < 0) {
this._count = 0;
}
return value;
};

// O(1)
MinStack.prototype.peek = function() {
return this._storage[this._count-1];
}

// O(1)
MinStack.prototype.count = function() {
return this._count;
};

MinStack.prototype.min = function() {
return this._min.peek();
}

var myMinStack = new MinStack(3);
console.log(myMinStack.push(1), 'should be 1');
console.log(myMinStack.push(2), 'should be 2');
console.log(myMinStack.push(3), 'should be 3');
console.log(myMinStack.min(), 'should be 1');
console.log(myMinStack.push(4), 'should be Max capacity reached');
console.log(myMinStack.pop(), 'should be 3');
console.log(myMinStack.count(), 'should be 2');
console.log(myMinStack.min(), 'should be 1');
console.log(myMinStack.peek(), 'should be 2');
console.log(myMinStack.count(), 'should be 2');