Variant of Binary Search to find low and High indices of a repeating number

Author: gokivego

arrays/findHighLowIndex.go

@@ -0,0 +1,56 @@
+/*
+Given a sorted array,find the low and high index of a number.
+Return -1 if the element is not found
+Array length can be large with a lot of duplicates
+*/
+
+package main
+
+import ("fmt"
+)
+
+// We can use binarySearch to solve this problem easily
+func findLowIndex(arr []int,searchNum int) int {
+    startIdx := 0
+    endIdx := len(arr) -1
+    mid := startIdx + (endIdx - startIdx)/2
+    for (startIdx <= endIdx) {
+        if arr[mid] < searchNum {
+            startIdx = mid+1
+        } else {
+            endIdx = mid-1
+        }
+        mid = startIdx + (endIdx - startIdx)/2
+    }
+    if arr[startIdx] == searchNum {
+        return startIdx
+    }
+    return -1
+}
+
+func findHighIndex(arr []int,searchNum int) int {
+    startIdx := 0
+    endIdx := len(arr) -1
+    mid := startIdx + (endIdx - startIdx)/2
+    for (startIdx <= endIdx) {
+        if arr[mid] > searchNum {
+            endIdx = mid-1
+        } else {
+            startIdx = mid+1
+        }
+        mid = startIdx + (endIdx - startIdx)/2
+    }
+    if arr[endIdx] == searchNum {
+        return endIdx
+    }
+    return -1
+}
+
+
+func main() {
+    arr := []int{1,2,5,5,5,5,5,5,5,5,20}
+    searchNum := 5
+    low := findLowIndex(arr,searchNum)
+    high := findHighIndex(arr,searchNum)
+    fmt.Println("Indices of number:",searchNum,"Low:",low,"High:",high)
+}