1 问题
给定一个数组和滑动窗口的大小，请找出所有滑动窗口里的最大值，列如，数组｛2,3,4,2,6,2,5,1｝的滑动窗口大小是3，一起6个滑动窗口，分别是{4，4，6，6，5}
2 分析
2,3,4,2,6,2,5,1
我们这里可以用双端队列，滑动窗口是3，我们先找出前3个数字里面的最大值，放在双端队列的头，然后依次向右滑动，确保每次滑动后队列的头是最大值。
3 代码实现
#include <iostream>
#include <vector>
#include <deque>using namespace std;vector<int> maxWindows(const vector<int> &nums, int size)
{vector<int> maxWindows;if (size <= 0 || nums.size() <= 0 || (nums.size() < size)){return maxWindows;}deque<int> indexs;for (int i = 0; i < size; ++i){while (indexs.size() > 0 && nums[i] > nums[indexs.back()]){indexs.pop_back();}indexs.push_back(i);}for (int i = size; i < nums.size(); ++i){maxWindows.push_back(nums[indexs.front()]);while (indexs.size() > 0 && nums[i] > nums[indexs.back()]){indexs.pop_back();}while (indexs.size() > 0 && (i - indexs.front() >= size)){indexs.pop_front(); }indexs.push_back(i);}maxWindows.push_back(nums[indexs.front()]);return maxWindows;
}int main()
{vector<int> nums;nums.push_back(2);nums.push_back(3);nums.push_back(4);nums.push_back(2);nums.push_back(6);nums.push_back(5);nums.push_back(2);nums.push_back(1);vector<int> result;result = maxWindows(nums, 3);if (result.size() > 0){for (int i = 0; i < result.size(); ++i)std::cout << result[i] << std::endl;}return 0;
}
4 运行结果
4
4
6
6
6
5
5 总结
在一个数组里面，通过双端队列（qedue）求最大值
std::deque<int> indexs;std::vector<int> nums;nums.push_back(1);nums.push_back(3);nums.push_back(2);nums.push_back(5);nums.push_back(4);for (int i = 0; i < nums.size(); ++i){while (indexs.size() > 0 && nums[i] > nums[indexs.back()]){indexs.pop_back();}indexs.push_back(i);}std::cout << "maxValue is " << nums[indexs.front()] << std::endl;
