常数时间取得min值的栈

设计这样的栈，常数时间内操作min，push，pop

/* * Copyright (c) 2011 alexingcool. All Rights Reserved. */ #include <iostream> #include <vector> #include <iterator> #include <algorithm> using namespace std; class Stack { public: Stack(int i = -1) : countItem(i + 1), maxPos(i) {} void push(int data) { if(countItem > 100) { cerr << "Stack is full" << endl; return; } if(maxPos == -1) { maxPos++; lastMaxPos[maxPos] = countItem; } else { if(data < item[lastMaxPos[maxPos]]) { maxPos++; lastMaxPos[maxPos] = countItem; } } item[countItem] = data; countItem++; } void pop() { if(countItem == 0) { cerr << "Stack is empty" << endl; return; } if(item[countItem - 1] == item[lastMaxPos[maxPos]]) { maxPos--; } countItem--; } int getMin() { if(maxPos != -1) return item[lastMaxPos[maxPos]]; else { cerr << "wrong" << endl; return -1; } } bool empty() { if(countItem == 0) return true; else return false; } private: static const int size = 100; int item[size]; int lastMaxPos[size]; int countItem; int maxPos; }; void main() { Stack stack; int array[] = {1, -2, 3, 7, -4, 10, 2, -5}; const int size = sizeof array / sizeof *array; for(int i = 0; i < size; i++) { stack.push(array[i]); cout << "min: " << stack.getMin() << endl; } cout << "---------------------------------------" << endl; while(!stack.empty()) { cout << "min: " << stack.getMin() << endl; stack.pop(); } }

 

又看了下编程之美关于此题的解法，总觉得太过繁琐，实际上只需要用一个数组来保存历届最小值即可，还可以省略掉一个下标，不需要如此麻烦。

/*  
* Copyright (c) 2011 alexingcool. All Rights Reserved.  
*/ 
#include <iostream>

using namespace std;

class Stack {
public:
	Stack(int i = - 1) : position(i) {}

	void push(int item) {
		if(position == size - 1) {
			cout << "Over Flow" << endl;
			return;
		}
	
		position++;
		data[position] = item;
		
		if(position == 0) {
			minValues[position] = item; 
		} else {
			if(item < minValues[position - 1])
				minValues[position] = item;
			else
				minValues[position] = minValues[position - 1];
		}
	}

	void pop() {
		if(position == -1) {
			cout << "under flow" << endl;
			return;
		}

		position--;
	}

	int min() { 
		if(position < 0 || position >= size) {
			cout << "wrong" << endl;
			return 0x80000000;
		}

		return minValues[position]; 
	}

	bool empty() {
		if(position == -1)
			return true;
		else
			return false;
	}

private:
	static const int size = 20;
	int data[size];
	int position;
	int minValues[size];
};

void main()
{
	Stack stack;
	int array[] = {5, 7, 3, 1, 2, 8, 4, 6};
	const int size = sizeof array / sizeof *array;

	for(int i = 0; i < size; i ++) {
		stack.push(array[i]);
		cout << stack.min() << "  ";
	}

	cout << endl;

	while(!stack.empty()) {
		cout << stack.min() << "  ";
		stack.pop();
	}
}