标签:des style blog color ar sp java strong div
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.
这个问题挺简单(确实leetcode给的评级也是easy),但是还真是遇上了不少的问题。
首先,这道题目我们的想法是如何去做到这个特殊的getMin,想到的方法当然是空间换时间啦,那么用什么空间呢?当然是另一个栈啦,所以我们就有了这么一个想法:用另一个栈来记录当前最小值,那么查找最小值就不需要遍历了,这样就实现了时间复杂度和空间复杂度都是O(n)。的确这个想法已经很不错了,用java(官方题解就是这个版本)和C++(亲测)。但是我用python就MLE了,让我纠结了好久。
所以在没办法就要优化内存了,这里采用的方法是在minStack中插值的时候对相同的值不重复插入,而是记录他的次数,终于AC
MLE
1 class MinStack: 2 def __init__(self): 3 self.stack = [] 4 self.minStack = [] 5 # @param x, an integer 6 # @return an integer 7 def push(self, x): 8 self.stack.append(x) 9 if len(self.minStack) == 0 or self.minStack[-1] >= x: 10 #print ‘minn change‘ 11 self.minStack.append(x) 12 13 # @return nothing 14 def pop(self): 15 p = self.stack.pop() 16 #print ‘pop ‘ , p 17 if p == self.minStack[-1]: 18 #print ‘minn pop‘ 19 self.minStack.pop() 20 21 # @return an integer 22 def top(self): 23 return self.stack[-1] 24 25 # @return an integer 26 def getMin(self): 27 return self.minStack[-1]
AC
1 class MinStack: 2 def __init__(self): 3 self.stack = [] 4 self.minStack = [] 5 #self.minStack.append(0) 6 # @param x, an integer 7 # @return an integer 8 def push(self, x): 9 self.stack.append(x) 10 if len(self.minStack) == 0 or self.minStack[-1][0] > x: 11 #print ‘minn change‘ 12 self.minStack.append((x,1)) 13 elif x == self.minStack[-1][0]: 14 self.minStack[-1] = (x, self.minStack[-1][1] + 1) 15 16 # @return nothing 17 def pop(self): 18 p = self.stack.pop() 19 #print ‘pop ‘ , p 20 if p == self.minStack[-1][0]: 21 if self.minStack[-1][1] > 1: 22 #print ‘minn pop‘ 23 self.minStack[-1] = (self.minStack[-1][0], self.minStack[-1][1] - 1) 24 else: 25 self.minStack.pop() 26 27 # @return an integer 28 def top(self): 29 return self.stack[-1] 30 31 # @return an integer 32 def getMin(self): 33 #print self.minStack 34 return self.minStack[-1][0]
【leetcode】Min Stack -- python版
标签:des style blog color ar sp java strong div
原文地址:http://www.cnblogs.com/MrLJC/p/4104709.html