剑指offer--面试题21：包含min函数的栈



题目描述

定义栈的数据结构，请在该类型中实现一个能够得到栈最小元素的min函数。 python实现：

# -*- coding:utf-8 -*-
class Solution:
    def __init__(self):
        self.stack = []
        self.min_stack = []
        
    def push(self, node):
        # write code here
        self.stack.append(node)
        if len(self.min_stack)>0: # 空栈
            node = min(node, self.min_stack[-1]) # 与栈顶比较
        self.min_stack.append(node)
        
    def pop(self):
        # write code here
        if len(self.stack)>0:
            self.min_stack.pop()
            return self.stack.pop()
        else: # 空栈
            raise Exception("Error: empty stack!")
        
    def top(self):
        # write code here
        if len(self.stack)>0:
            return self.stack[-1]
        else:
            raise Exception("Error: empty stack!")
        
    def min(self):
        # write code here
        if len(self.min_stack)>0:
            return self.min_stack[-1]
        else:
            raise Exception("Error: empty stack!")
           

c++实现：

class Solution {
private:
    vector<int> stack;
    vector<int> minStack;
public:
    void push(int value) {
        stack.push_back(value);
        if(!minStack.empty()){
            int top = minStack.back();
            value = std::min(top, value);
        }
        minStack.push_back(value);
    }
     
    void pop() {
        if(!stack.empty()){
            stack.pop_back();
            minStack.pop_back();
        }
    }
     
    int top() {
        if(!stack.empty()){
            return stack.back();
        }
        return NULL;
    }
    int min() {
        if(!minStack.empty()){
            return minStack.back();
        }
        return NULL;
    }
};