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: $O(1)$
• Space Complexity: $O(1)$