Tuesday, February 3, 2015

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();
 */
at

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