Add C++ solution of problem #3105

Author: Cuda-Chen

3105/solution.cpp

@@ -0,0 +1,31 @@
+class Solution {
+public:
+    int longestMonotonicSubarray(vector<int>& A) {
+        int in = 0, de = 0; // max len of strictly increasing/decreasing
+        int tmp = 0; // previous element
+        int ans = 1;
+        for(int i = 0; i < A.size(); i++) {
+            if(i == 0) {
+                in = de = 1;
+                tmp = A[i];
+                continue;
+            }
+
+            // increasing
+            if(A[i] > tmp)
+                in++;
+            else
+                in = 1;
+
+            // decreasing
+            if(A[i] < tmp)
+                de++;
+            else
+                de = 1;
+
+            tmp = A[i];
+            ans = max({ans, in, de});
+        }
+        return ans;
+    }
+};