1+ /**
2+ * This file contain an implementation of the maximum sliding window problem. This code has been
3+ * tested against the judge data on:
4+ *
5+ * <p>https://leetcode.com/problems/sliding-window-maximum/description/
6+ *
7+ * @author William Fiset, william.alexandre.fiset@gmail.com
8+ */
9+ 10+ import java .util .ArrayDeque ;
11+ import java .util .Deque ;
12+ 13+ public class SlidingWindowMaximum {
14+ 15+ int [] values ;
16+ public int N , lo , hi ;
17+ 18+ Deque <Integer > deque = new ArrayDeque <>();
19+ 20+ public SlidingWindowMaximum (int [] values ) {
21+ if (values == null ) throw new IllegalArgumentException ();
22+ this .values = values ;
23+ N = values .length ;
24+ }
25+ 26+ // Advances the front of the window by one unit
27+ public void advance () {
28+ 29+ // Remove all the worse values in the back of the deque
30+ while (!deque .isEmpty () && values [deque .peekLast ()] < values [hi ])
31+ deque .removeLast (); // Change the '<' sign here ^^^ to '>' for minimum sliding window
32+ 33+ // Add the next index to the back of the deque
34+ deque .addLast (hi );
35+ 36+ // Increase the window size
37+ hi ++;
38+ }
39+ 40+ // Retracks the back of the window by one unit
41+ public void shrink () {
42+ 43+ // Decrease window size by pushing it forward
44+ lo ++;
45+ 46+ // Remove elements in the front of the queue whom are no longer
47+ // valid in the reduced window.
48+ while (!deque .isEmpty () && deque .peekFirst () < lo ) deque .removeFirst ();
49+ }
50+ 51+ // Query the current maximum value in the window
52+ public int getMax () {
53+ if (lo >= hi ) throw new IllegalStateException ("Make sure lo < hi" );
54+ return values [deque .peekFirst ()];
55+ }
56+ }
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