155.Min Stack

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Stack, Easy

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:

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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.

My Answer

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class MinStack {
    Stack<Integer> stack = new Stack<>();
    Stack<Integer> min = new Stack<>();
    /** initialize your data structure here. */
    public MinStack() {
        
    }
    
    public void push(int x) {
        if(min.isEmpty() || x<=min.peek())
            min.push(x);
        stack.push(x);
    }
    
    public void pop() {
        if(stack.peek().equals(min.peek()))
            min.pop();
        stack.pop();
    }
    
    public int top() {
        return stack.peek();
    }
    
    public int getMin() {
        return min.peek();
    }
}
/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(x);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */

Running time: 101ms