LeetCode(155)题解--Min Stack

https://leetcode.com/problems/min-stack/

题目：

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.

思路：

关键在于找最小值要O(1)复杂度，所以空间换时间。一个额外的vector存储递减序入栈的数字。

AC代码：

 class MinStack {
 public:
     MinStack(){ st_min.push_back(INT_MAX); };
     void push(int x) {
         if (x <= st_min[st_min.size()-])
             st_min.push_back(x);
         st.push_back(x);
         return;
     }

     void pop() {
         if (st[st.size() - ] == st_min[st_min.size() - ]){
             st_min.pop_back();
         }
         st.pop_back();
         return;
     }

     int top() {
         return st[st.size() - ];
     }

     int getMin() {
         return st_min[st_min.size() - ];
     }

 private:
     vector<int> st;
     vector<int> st_min;
 };