LeetCode [155] Min Stack

155. Min Stack

Easy

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 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:

• Methods pop, top and getMin operations will always be called on non-empty stacks.

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class MinStack { stack<int> stk, stkm; public: /** initialize your data structure here. */ MinStack() { } void push(int x) { stk.push(x); if(stkm.empty()) stkm.push(x); else{ if(stkm.top()>=x) stkm.push(x); } } void pop() { int x = stk.top(); stk.pop(); if(x==stkm.top()) stkm.pop(); } int top() { return stk.top(); } int getMin() { return stkm.top(); } }; /** * 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(); */