Add problem 1991: Find the Middle Index in Array

src/lib.rs

@@ -1378,6 +1378,7 @@ pub mod problem_1979_find_greatest_common_divisor_of_array;
 pub mod problem_1980_find_unique_binary_string;
 pub mod problem_1984_minimum_difference_between_highest_and_lowest_of_k_scores;
 pub mod problem_1985_find_the_kth_largest_integer_in_the_array;
+pub mod problem_1991_find_the_middle_index_in_array;
 
 #[cfg(test)]
 mod test_utilities;

src/problem_1991_find_the_middle_index_in_array/iterative.rs

@@ -0,0 +1,39 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn find_middle_index(nums: Vec<i32>) -> i32 {
+        let total_sum = nums.iter().sum::<i32>();
+        let mut result = -1;
+        let mut sum = 0;
+
+        for (i, num) in (0..).zip(nums) {
+            if sum + sum + num == total_sum {
+                result = i;
+
+                break;
+            }
+
+            sum += num;
+        }
+
+        result
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn find_middle_index(nums: Vec<i32>) -> i32 {
+        Self::find_middle_index(nums)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_1991_find_the_middle_index_in_array/mod.rs

@@ -0,0 +1,18 @@
+pub mod iterative;
+
+pub trait Solution {
+    fn find_middle_index(nums: Vec<i32>) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [(&[2, 3, -1, 8, 4] as &[_], 3), (&[1, -1, 4], 2), (&[2, 5], -1)];
+
+        for (nums, expected) in test_cases {
+            assert_eq!(S::find_middle_index(nums.to_vec()), expected);
+        }
+    }
+}