《剑指offer》65：滑动窗口的最大值

题目：给定一个数组和滑动窗日的大小，请找出所有滑动窗口里的最大值。如果输入数组{2,3,4,2,6,2,5,1}及滑动窗印的大小3，那么存在6个滑动窗口，它们的最大值分别为{4,4,6,6,6,5}。

第一想法是按窗口滑动，每次对比窗口内的数字大小，选出最大值，但很明显，这里存在着很多次重复的大小对比操作，将那些重复的操作想办法剪去即可。

#include<iostream>
#include<vector>
#include<queue>
using namespace std;

vector<int> maxnum_in_window(const vector<int>& data, unsigned int windowsize)
{
	vector<int> maxnum;
	if (windowsize <= data.size() && windowsize >= 1){
		deque<int> index;

		for (unsigned int i = 0; i < windowsize; ++i){
			while (!index.empty() && data[i] >= data[index.back()])
				index.pop_back();
			index.push_back(i);
		}
		for (unsigned int i = windowsize; i < data.size(); ++i){
			maxnum.push_back(data[index.front()]);

			while (!index.empty() && data[i] >= data[index.back()])
				index.pop_back();
			if (!index.empty() && index.front() <= (i - windowsize))
				index.pop_front();

			index.push_back(i);
		}
		maxnum.push_back(data[index.front()]);
	}
	return maxnum;
}

void test(char* testname, vector<int>& T, unsigned int windowsize)
{
	cout << endl << "----" << testname << "----" << endl;
	vector<int> maxnum = maxnum_in_window(T, windowsize);
	for (unsigned int i = 0; i < maxnum.size(); ++i){
		cout << maxnum[i] << ",";
	}
}
void test1()
{
	vector<int> T1 = { 2, 3, 4, 2, 6, 2, 5, 1 };
	unsigned int windowsize = 3;
	test("test1", T1, windowsize);
}
int main(int argc, char* argv[])
{
	test1();
	system("pause");
	return 0;
}