Add valid-mountain-array

Author: Gituser143

Easy/valid-mountain-array.md

@@ -0,0 +1,49 @@
+Code
+====
+
+```go
+func validMountainArray(arr []int) bool {
+	if len(arr) < 3 {
+		return false
+	}
+
+	n := len(arr)
+
+	i := 0
+	for i = 0; i < n-1; i++ {
+		if arr[i] >= arr[i+1] {
+			break
+		}
+	}
+
+	if i == 0 {
+		return false
+	}
+
+	j := i
+	for j = i + 1; j < n; j++ {
+		if arr[j] >= arr[j-1] {
+			return false
+		}
+	}
+
+	if j == i+1 {
+		return false
+	}
+
+	return true
+}
+```
+
+Solution in mind
+================
+
+-	Solution is a simple one pass traversal of the array.
+
+-	As we climb p the array we ensure that `arr[i+1] >= arr[i]`. When this is violated, we reach a peak.
+
+-	We must ensure the peak is not at the very beginning (`i == 0`), if it was, we never climbed up the mountain.
+
+-	After reaching peak, we begin to climb down, while ensuring the condition `arr[i] < arr[i-1]`, if not, we either have a rise or flat zone in the mountain.
+
+-	After descending from the peak, we ensure we have actually moved downwards and not stayed at the peak (`j == i+1`). This acts as a check to ensure the peak is not at the very end of the array too.

README.md

@@ -5,7 +5,7 @@ My collection of leet code problems solved in GoLang!
 
 | [Easy](#easy) | [Medium](#medium) | [Hard](#hard) |
 |---------------|-------------------|---------------|
-| 32            | 48                | 10            |
+| 33            | 48                | 10            |
 
 Problems finished
 =================
@@ -77,6 +77,8 @@ Easy
 
 -	[best-time-to-buy-and-sell-stock](Easy/best-time-to-buy-and-sell-stock.md)
 
+-	[valid-mountain-array](Easy/valid-mountain-array.md)
+
 Medium
 ------