[JS][7kyu] Sensor Trend Reversals

codewars/7kyu/sensor-trend-reversals/koronya.js

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+// [JS][7kyu] Sensor Trend Reversals
+// sensor-trend-reversals
+// https://www.codewars.com/kata/6a6bdaca77f722e42da8fba6/train/javascript
+
+const removeDuplicateContinuousArr = (arr) => {
+  const arrLen = arr.length
+  if (arrLen < 2) {
+    return arr
+  }
+  let prev = arr[0]
+  const result = [prev]
+  for (let i = 1; i < arrLen; i += 1) {
+    const now = arr[i]
+    if (now !== prev) {
+      result.push(now)
+    }
+    prev = now
+  }
+  return result
+}
+
+const countDirectionChanges = (readings) => {
+  const modifyArr = removeDuplicateContinuousArr(readings)
+  const modifyArrLen = modifyArr.length
+  if (modifyArrLen < 2) {
+    return 0
+  }
+
+  let count = 0
+  let isIncreasing = modifyArr[0] < modifyArr[1]
+  let prev = modifyArr[1]
+  for (let i = 2; i < modifyArrLen; i += 1) {
+    const now = modifyArr[i]
+    if (isIncreasing) {
+      if (now < prev) {
+        count += 1
+      }
+    } else {
+      if (now > prev) {
+        count += 1
+      }
+    }
+    isIncreasing = prev < now
+    prev = now
+  }
+
+  return count
+}
+
+// countDirectionChanges([1, 3, 2, 4])
+// countDirectionChanges([1, 3, 2, 4]) === 2
+// countDirectionChanges([5, 3, 1]) === 0
+// countDirectionChanges([1, 1, 3, 3, 2]) === 1
+// countDirectionChanges([4, 4, 4]) === 0
+// countDirectionChanges([]) === 0