First and last in sorted array

Author: ratulb

codes/find_first_last.mojo

@@ -0,0 +1,52 @@
+### Find First/Last
+### Find first and last index of a target value in a sorted array
+
+
+fn find_first_last(arr: List[Int], target: Int) -> (Int, Int):
+    result = (-1, -1)
+    if len(arr) == 0:
+        return result
+    left, right = 0, len(arr) - 1
+
+    while left <= right:
+        mid = (left + right) // 2
+        if arr[mid] == target:
+            result[1] = mid
+            left = mid + 1
+        elif arr[mid] > target:
+            right = mid - 1
+        else:
+            left = mid + 1
+    left, right = (
+        0,
+        result[1],
+    )  # result[1] -1 would keep left index at -1 for single occurence of target
+
+    while left <= right:
+        mid = (left + right) // 2
+        if arr[mid] == target:
+            result[0] = mid
+            right = mid - 1
+        elif arr[mid] > target:
+            right = mid - 1
+        else:
+            left = mid + 1
+    return result
+
+
+from testing import assert_true
+
+
+fn main() raises:
+    arr = List(5, 7, 7, 8, 8, 10)
+    target = 8
+    result = find_first_last(arr, target)
+    assert_true(result[0] == 3 and result[1] == 4, "Assertion failed")
+    target = 6
+    result = find_first_last(arr, target)
+    assert_true(result[0] == -1 and result[1] == -1, "Assertion failed")
+
+    arr = List(5, 7, 7, 8, 10)
+    target = 8
+    result = find_first_last(arr, target)
+    assert_true(result[0] == 3 and result[1] == 3, "Assertion failed")

docs/find_first_last.md

@@ -0,0 +1,59 @@
+### Find First/Last
+### Find first and last index of a target value in a sorted array
+
+```python
+
+
+fn find_first_last(arr: List[Int], target: Int) -> (Int, Int):
+    result = (-1, -1)
+    if len(arr) == 0:
+        return result
+    left, right = 0, len(arr) - 1
+
+    while left <= right:
+        mid = (left + right) // 2
+        if arr[mid] == target:
+            result[1] = mid
+            left = mid + 1
+        elif arr[mid] > target:
+            right = mid - 1
+        else:
+            left = mid + 1
+    left, right = (
+        0,
+        result[1],
+    )  # result[1] -1 would keep left index at -1 for single occurence of target
+
+    while left <= right:
+        mid = (left + right) // 2
+        if arr[mid] == target:
+            result[0] = mid
+            right = mid - 1
+        elif arr[mid] > target:
+            right = mid - 1
+        else:
+            left = mid + 1
+    return result
+
+
+from testing import assert_true
+
+
+fn main() raises:
+    arr = List(5, 7, 7, 8, 8, 10)
+    target = 8
+    result = find_first_last(arr, target)
+    assert_true(result[0] == 3 and result[1] == 4, "Assertion failed")
+    target = 6
+    result = find_first_last(arr, target)
+    assert_true(result[0] == -1 and result[1] == -1, "Assertion failed")
+
+    arr = List(5, 7, 7, 8, 10)
+    target = 8
+    result = find_first_last(arr, target)
+    assert_true(result[0] == 3 and result[1] == 3, "Assertion failed")
+
+```
+
+
+[Source](https://github.com/ratulb/mojo_programming/blob/main/codes/find_first_last.mojo)

docs/index.md

@@ -65,4 +65,6 @@
 
 🟢 [Largest Number](largest_number.md) ➔ Arrange non-negative integers to form the largest possible number and return it as a string.
 
-🟢 [Find All Anagrams in a String](all_anagrams.md) ➔ Return all start indices of anagrams of string p in string s.
+🟢 [Find All Anagrams in a String](all_anagrams.md) ➔ Return all start indices of anagrams of string p in string s.
+
+🟢 [Find First/Last](find_first_last.md) ➔ Find first and last index of a target value in a sorted array