Min Stack

Desicription

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.

Solution

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/**
* 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();
*/
class MinStack {
private:
stack<int> numStack;
stack<int> minStack;
public:
void push(int x) {
if(minStack.empty() || x <= minStack.top())
minStack.push(x);
numStack.push(x);
}
void pop() {
if(numStack.top() == minStack.top())
minStack.pop();
numStack.pop();
}
int top() {
return numStack.top();
}
int getMin() {
return minStack.top();
}
};