239. max sliding window

Author: jiofeng

239MaxSlidingWindow/MaxSlidingWindow.java

@@ -0,0 +1,63 @@
+import java.util.Deque;
+import java.util.LinkedList;
+
+/**
+ * @author jiofeng
+ * @date 2020/3/3
+ */
+public class MaxSlidingWindow {
+    public static void main(String[] args) {
+//        int[] nums = {1, 3, 1, 2, 0, 5};
+        int[] nums = {1, 3, -1, -3, 5, 3, 6, 7};
+//        int[] nums = {1, -1};
+        int[] res = new MaxSlidingWindowSolution().maxSlidingWindow(nums, 3);
+        for (int num : res) {
+            System.out.println(num);
+        }
+    }
+}
+
+class MaxSlidingWindowSolution {
+    public int[] maxSlidingWindow(int[] nums, int k) {
+        if (nums.length == 0) {
+            return new int[0];
+        }
+        Deque<Integer> deque = new LinkedList<>();
+        // init deque
+        for (int i = 0; i < k; i++) {
+            putInDeque(deque, nums, i, k);
+        }
+        int[] resIndexes = new int[nums.length - k + 1];
+        for (int i = k; i < nums.length; i++) {
+            resIndexes[i - k] = deque.peekFirst();
+            putInDeque(deque, nums, i, k);
+        }
+        // last one
+        resIndexes[resIndexes.length - 1] = deque.peekFirst();
+        // construct result
+        int[] res = new int[nums.length - k + 1];
+        for (int i = 0; i < resIndexes.length; i++) {
+            res[i] = nums[resIndexes[i]];
+        }
+        return res;
+    }
+
+    private void putInDeque(Deque<Integer> deque, int[] nums, int i, int k) {
+        if (deque.isEmpty()) {
+            deque.add(i);
+            return;
+        }
+        // window is full
+        if (i - deque.peekFirst() == k) {
+            deque.pollFirst();
+        }
+        if (!deque.isEmpty() && nums[deque.peekFirst()] <= nums[i]) {
+            deque.clear();
+        }
+        // poll the num in deque of loe num
+        while (!deque.isEmpty() && nums[deque.peekLast()] <= nums[i]) {
+            deque.pollLast();
+        }
+        deque.add(i);
+    }
+}