*

coding_interviews/algoexpert/monotonic-array/monotonic-array-optimization-1.js

@@ -0,0 +1,42 @@
+/**
+ * Write a function that takes in an array of integers and returns a boolean
+ * representing whether the array is monotonic.
+ * An array is said to be monotonic if its elements, from left to right, are
+ * entirely non-increasing or entirely non-decreasing.
+ * Non-increasing elements aren't necessarily exclusively decreasing; they
+ * simply don't increase. Similarly, non-decreasing elements aren't necessarily
+ * exclusively increasing; they simply don't decrease.
+ * Note that empty arrays and arrays of one element are monotonic.
+ *
+ * Input:
+ * array = [-1, -5, -10, -1100, -1100, -1101, -1102, -9001]
+ *
+ * Output:
+ * true
+ */
+
+// Runtime: O(N), N = array length
+// Space: O(1)
+
+function isMonotonic(array) {
+  let num = array[0];
+  let upward;
+
+  for (let index = 1; index < array.length; index++) {
+    if (upward === undefined) {
+      upward = array[index] !== num ? array[index] > num : undefined;
+    }
+
+    if (upward !== undefined && upward && array[index] < num) {
+      return false;
+    }
+
+    if (upward !== undefined && !upward && array[index] > num) {
+      return false;
+    }
+
+    num = array[index];
+  }
+
+  return true;
+}