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.
提示：提交代码后，需要用简洁的语言解释一下代码思路~ 谢谢
历史题目和总结见公众号「每日一道算法题」
https://leetcode.com/problems/min-stack/#/description
思路一：
用 hash 来保存当前的值 和 与其对应的 最小值。
时间复杂度： O(1)；空间复杂度：O(N)
