feat(leetcode): add No.2765

Author: mickey0524

2765.Longest-Alternating-Subarray.java

@@ -0,0 +1,43 @@
+// https://leetcode.com/problems/longest-alternating-subarray/
+// algorithms
+// Easy (32.6%)
+// Total Accepted: 14.9K
+// Total Submissions: 45.6K
+
+class Solution {
+
+    public int alternatingSubarray(int[] nums) {
+        int len = nums.length;
+        if (len < 2) {
+            return -1;
+        }
+
+        int diff = 1;
+        int curSubArrLen = 1;
+        int res = -1;
+        for (int i = 1; i < len; i++) {
+            if (nums[i] - nums[i - 1] == diff) {
+                curSubArrLen++;
+                diff = -diff;
+            } else if (curSubArrLen > 1) {
+                res = Math.max(res, curSubArrLen);
+
+                if (nums[i] - nums[i - 1] == -diff) {
+                    curSubArrLen = 2;
+                } else {
+                    curSubArrLen = 1;
+                    diff = 1;
+                }
+            }
+        }
+
+        if (curSubArrLen > 1) {
+            res = Math.max(res, curSubArrLen);
+        } 
+
+        return res;
+    }
+
+}
+
+// [14,30,29,49,3,23,44,21,26,52]