155. Min Stack

155. Min Stack (Easy)

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.

 

Related Topics:
Stack, Design

Similar Questions:

• Sliding Window Maximum (Hard)
• Max Stack (Easy)

Solution 1.

// OJ: https://leetcode.com/problems/min-stack/
// Author: github.com/lzl124631x
// Time: O(1) for all
// Space: O(N)
class MinStack {
    stack<int> mn;
    stack<int> val;
public:
    MinStack() {}
    void push(int x) {
        val.push(x);
        if (mn.empty() || mn.top() >= x) mn.push(x);
    }
    void pop() {
        if (val.top() == mn.top()) mn.pop();
        val.pop();
    }
    int top() {
        return val.top();
    }
    int getMin() {
        return mn.top();
    }
};