leetcode-155-min stack

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.

设计一个栈，支持push,pop,top和在O(1)时间内找到最小值。

利用一个栈存储到此为止的最小值。注意如果有重复的最小值需要多次push，因为如果出现3 2 1 2 1这样的用例，若不重复入栈则会出错。

class MinStack {
public:
stack<int> st;
stack<int> minSt;
    /** initialize your data structure here. */
    MinStack() {

    }

    void push(int x) {
        st.push(x);
        if(minSt.empty()||x<=minSt.top()) minSt.push(x);
    }

    void pop() {
        if(minSt.top()==st.top()) minSt.pop();
        st.pop();
    }

    int top() {
        return st.top();
    }

    int getMin() {
        return minSt.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();
 */