LeetCode 155. Min Stack

 155. Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Implement the MinStack class:

• MinStack() initializes the stack object.
• void push(int val) pushes the element val onto the stack.
• void pop() removes the element on the top of the stack.
• int top() gets the top element of the stack.
• int getMin() retrieves the minimum element in the stack.

 

Example 1:

Input
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]

Output
[null,null,null,null,-3,null,0,-2]

Explanation
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); // return -3
minStack.pop();
minStack.top();    // return 0
minStack.getMin(); // return -2

 

Constraints:

• -231 <= val <= 231 - 1
• Methods pop, top and getMin operations will always be called on non-empty stacks.
• At most 3 * 104 calls will be made to push, pop, top, and getMin.

	class MinStack {
	public:
	// keep with min value
	stack<pair<int, int>> st;
	MinStack() {
	}
	void push(int val) {
	if(st.empty()) st.push({val, val});
	else st.push({val, min(val, st.top().second)});
	}
	void pop() {
	st.pop();
	}
	int top() {
	return st.top().first;
	}
	int getMin() {
	return st.top().second;
	}
	};
	/**
	* Your MinStack object will be instantiated and called as such:
	* MinStack* obj = new MinStack();
	* obj->push(val);
	* obj->pop();
	* int param_3 = obj->top();
	* int param_4 = obj->getMin();
	*/

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