MinStack.java

// Time Complexity : O(1)
// Space Complexity : O(n)
// Did this code successfully run on Leetcode : Yes
// Any problem you faced while coding this : No

// Approach:
// Use two stacks: one to store values and another to track the minimum at each level.
// On every push, store the current minimum so getMin is always O(1).
// On pop, remove from both stacks to keep them in sync.

import java.util.Stack;

class MinStack {
    Stack<Integer> st;
    Stack<Integer> minSt;
    int min;

    public MinStack() {
        this.st = new Stack<>();
        this.minSt = new Stack<>();
        this.min = Integer.MAX_VALUE;
        minSt.push(min);
    }
    
    public void push(int val) {
        min = Math.min(val,min);
        st.push(val);
        minSt.push(min);
    }
    
    public void pop() {
        st.pop();
        minSt.pop();
        min = minSt.peek();
    }
    
    public int top() {
        return st.peek();
    }
    
    public int getMin() {
        return min;
    }
}