Min Stack

07/15/2016 Stack Design

Question

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.

Solution

Result: Accepted Time: 28 ms

Here should be some explanations.

class MinStack {
    stack<int> sta;
    stack<int> min_sta;
public:
    void push(int x) {
        sta.push(x);
        if(min_sta.empty())
        {
            min_sta.push(x);
            return;
        }
        min_sta.push(min(min_sta.top(),x));
    }

    void pop() {
        sta.pop();
        min_sta.pop();
    }

    int top() {
        return sta.top();
    }

    int getMin() {
        return min_sta.top();
    }
};

Complexity Analytics

  • Time Complexity:
  • Space Complexity: