如何解决最大滑动窗口问题我的解决方案无效,但非常相似的解决方案有效,而且我不明白为什么
我正在尝试解决“滑动窗口最大值”问题(给定一个数组和一个整数m,为每个大小为m的连续子数组找到最大值)。
我实际上设法解决了这个问题,但是我的代码对于一个测试用例来说太慢了。在geeksforgeeks上,我找到了与我的解决方案非常相似的解决方案,但是它可以正常工作,我不明白为什么。有人知道发生了什么吗?
我正在用Java编程,这是两个代码:
我的:
public static void solve(int[] a,int m) {
int n = a.length;
arraydeque<Integer> pico = new arraydeque<Integer>();
for(int i = 0; i < m-1; i++) {
while(!pico.isEmpty() && a[pico.getLast()] <= a[i]) {
pico.removeLast();
}
pico.addLast(i);
}
for(int i = m-1; i < n; i++) {
while(!pico.isEmpty() && a[pico.getLast()] <= a[i]) {
pico.removeLast();
}
pico.addLast(i);
if(pico.getFirst()+m <= i) {
pico.removeFirst();
}
System.out.printf("%d ",a[pico.getFirst()]);
}
Geeksforgeeks:
static void printMax(int arr[],int n,int k)
{
// Create a Double Ended Queue,Qi that will store indexes of array elements
// The queue will store indexes of useful elements in every window and it will
// maintain decreasing order of values from front to rear in Qi,i.e.,// arr[Qi.front[]] to arr[Qi.rear()] are sorted in decreasing order
Deque<Integer> Qi = new LinkedList<Integer>();
/* Process first k (or first window) elements of array */
int i;
for (i = 0; i < k; ++i) {
// For every element,the prevIoUs smaller elements are useless so
// remove them from Qi
while (!Qi.isEmpty() && arr[i] >= arr[Qi.peekLast()])
Qi.removeLast(); // Remove from rear
// Add new element at rear of queue
Qi.addLast(i);
}
// Process rest of the elements,from arr[k] to arr[n-1]
for (; i < n; ++i) {
// The element at the front of the queue is the largest element of
// prevIoUs window,so print it
System.out.print(arr[Qi.peek()] + " ");
// Remove the elements which are out of this window
while ((!Qi.isEmpty()) && Qi.peek() <= i - k)
Qi.removeFirst();
// Remove all elements smaller than the currently
// being added element (remove useless elements)
while ((!Qi.isEmpty()) && arr[i] >= arr[Qi.peekLast()])
Qi.removeLast();
// Add current element at the rear of Qi
Qi.addLast(i);
}
// Print the maximum element of last window
System.out.print(arr[Qi.peek()]);
}
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