Add problem 852: Peak Index in a Mountain Array

Author: EFanZh

src/lib.rs

@@ -694,6 +694,7 @@ pub mod problem_0845_longest_mountain_in_array;
 pub mod problem_0846_hand_of_straights;
 pub mod problem_0848_shifting_letters;
 pub mod problem_0849_maximize_distance_to_closest_person;
+pub mod problem_0852_peak_index_in_a_mountain_array;
 pub mod problem_0867_transpose_matrix;
 pub mod problem_1143_longest_common_subsequence;
 pub mod problem_1192_critical_connections_in_a_network;

src/problem_0852_peak_index_in_a_mountain_array/binary_search.rs

@@ -0,0 +1,38 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn peak_index_in_mountain_array(arr: Vec<i32>) -> i32 {
+        let mut left = 1;
+        let mut right = arr.len() - 2;
+
+        while left < right {
+            let middle = (left + right) / 2;
+
+            if arr[middle] < arr[middle + 1] {
+                left = middle + 1;
+            } else {
+                right = middle;
+            }
+        }
+
+        left as _
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn peak_index_in_mountain_array(arr: Vec<i32>) -> i32 {
+        Self::peak_index_in_mountain_array(arr)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_0852_peak_index_in_a_mountain_array/iterative.rs

@@ -0,0 +1,25 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn peak_index_in_mountain_array(arr: Vec<i32>) -> i32 {
+        arr.iter().zip(&arr[1..]).position(|(lhs, rhs)| lhs > rhs).unwrap() as _
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn peak_index_in_mountain_array(arr: Vec<i32>) -> i32 {
+        Self::peak_index_in_mountain_array(arr)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_0852_peak_index_in_a_mountain_array/mod.rs

@@ -0,0 +1,24 @@
+pub mod iterative;
+
+pub trait Solution {
+    fn peak_index_in_mountain_array(arr: Vec<i32>) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            (&[0, 1, 0] as &[_], 1),
+            (&[0, 2, 1, 0], 1),
+            (&[0, 10, 5, 2], 1),
+            (&[3, 4, 5, 1], 2),
+            (&[24, 69, 100, 99, 79, 78, 67, 36, 26, 19], 2),
+        ];
+
+        for (arr, expected) in test_cases {
+            assert_eq!(S::peak_index_in_mountain_array(arr.to_vec()), expected);
+        }
+    }
+}