1991. Find the Middle Index in Array: AC

Author: tan-wei

src/solution/mod.rs

@@ -1499,3 +1499,4 @@ mod s1984_minimum_difference_between_highest_and_lowest_of_k_scores;
 mod s1985_find_the_kth_largest_integer_in_the_array;
 mod s1986_minimum_number_of_work_sessions_to_finish_the_tasks;
 mod s1987_number_of_unique_good_subsequences;
+mod s1991_find_the_middle_index_in_array;

src/solution/s1991_find_the_middle_index_in_array.rs

@@ -0,0 +1,95 @@
+/**
+ * [1991] Find the Middle Index in Array
+ *
+ * Given a 0-indexed integer array nums, find the leftmost middleIndex (i.e., the smallest amongst all the possible ones).
+ * A middleIndex is an index where nums[0] + nums[1] + ... + nums[middleIndex-1] == nums[middleIndex+1] + nums[middleIndex+2] + ... + nums[nums.length-1].
+ * If middleIndex == 0, the left side sum is considered to be 0. Similarly, if middleIndex == nums.length - 1, the right side sum is considered to be 0.
+ * Return the leftmost middleIndex that satisfies the condition, or -1 if there is no such index.
+ *  
+ * Example 1:
+ *
+ * Input: nums = [2,3,-1,<u>8</u>,4]
+ * Output: 3
+ * Explanation: The sum of the numbers before index 3 is: 2 + 3 + -1 = 4
+ * The sum of the numbers after index 3 is: 4 = 4
+ *
+ * Example 2:
+ *
+ * Input: nums = [1,-1,<u>4</u>]
+ * Output: 2
+ * Explanation: The sum of the numbers before index 2 is: 1 + -1 = 0
+ * The sum of the numbers after index 2 is: 0
+ *
+ * Example 3:
+ *
+ * Input: nums = [2,5]
+ * Output: -1
+ * Explanation: There is no valid middleIndex.
+ *
+ *  
+ * Constraints:
+ *
+ * 	1 <= nums.length <= 100
+ * 	-1000 <= nums[i] <= 1000
+ *
+ *  
+ * Note: This question is the same as 724: <a href="https://leetcode.com/problems/find-pivot-index/" target="_blank">https://leetcode.com/problems/find-pivot-index/</a>
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/find-the-middle-index-in-array/
+// discuss: https://leetcode.com/problems/find-the-middle-index-in-array/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    pub fn find_middle_index(nums: Vec<i32>) -> i32 {
+        let sum: i32 = nums.iter().sum();
+
+        let mut sum_cur: i32 = 0;
+
+        for (idx, num) in nums.into_iter().enumerate() {
+            if sum_cur == sum - sum_cur - num {
+                return idx as i32;
+            }
+            sum_cur += num;
+        }
+
+        -1
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1991_example_1() {
+        let nums = vec![2, 3, -1, 8, 4];
+
+        let result = 3;
+
+        assert_eq!(Solution::find_middle_index(nums), result);
+    }
+
+    #[test]
+    fn test_1991_example_2() {
+        let nums = vec![1, -1, 4];
+
+        let result = 2;
+
+        assert_eq!(Solution::find_middle_index(nums), result);
+    }
+
+    #[test]
+    fn test_1991_example_3() {
+        let nums = vec![2, 5];
+
+        let result = -1;
+
+        assert_eq!(Solution::find_middle_index(nums), result);
+    }
+}