Create valid-mountain-array.cpp

Author: kamyu104

C++/valid-mountain-array.cpp

@@ -0,0 +1,17 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    bool validMountainArray(vector<int>& A) {
+        int i = 0;
+        while (i + 1 < A.size() && A[i] < A[i + 1]) {
+            ++i;
+        }
+        int j = A.size() - 1;
+        while (j - 1 >= 0 && A[j - 1] > A[j]) {
+            --j;
+        }
+        return 0 < i && i == j && j < A.size() - 1;
+    }
+};