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minStackConstantTime.js
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minStackConstantTime.js
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/*
Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
push(x) -- Push element x onto stack.
pop() -- Removes the element on top of the stack.
top() -- Get the top element.
getMin() -- Retrieve the minimum element in the stack.
Example:
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); --> Returns -3.
minStack.pop();
minStack.top(); --> Returns 0.
minStack.getMin(); --> Returns -2.
*/
class MinStack {
constructor() {
this.stack = [];
}
push(x) {
let min = this.stack[0] ? this.stack[0].min : null;
if (min === null) this.stack.unshift({ val: x, min: x });
else {
this.stack.unshift({ val: x, min: Math.min(x, min) });
}
return this;
}
pop() {
this.stack.shift();
return this;
}
top() {
return this.stack.length ? this.stack[0].val : null;
}
getMin() {
return this.stack.length ? this.stack[0].min : null;
}
}
let minStack = new MinStack();
minStack.push(-2).push(-1);
minStack.push(0);
console.log(-2 === minStack.getMin());
console.log(0 === minStack.top());
minStack.push(-3);
console.log(-3 === minStack.getMin());
console.log(-3 === minStack.top(-3));
minStack.pop();
console.log(0 === minStack.top());
console.log(-2 === minStack.getMin());
console.log(minStack.stack);