1901. Find a Peak Element II: AC

Author: tan-wei

src/solution/mod.rs

@@ -1433,3 +1433,4 @@ mod s1897_redistribute_characters_to_make_all_strings_equal;
 mod s1898_maximum_number_of_removable_characters;
 mod s1899_merge_triplets_to_form_target_triplet;
 mod s1900_the_earliest_and_latest_rounds_where_players_compete;
+mod s1901_find_a_peak_element_ii;

src/solution/s1901_find_a_peak_element_ii.rs

@@ -0,0 +1,96 @@
+/**
+ * [1901] Find a Peak Element II
+ *
+ * A peak element in a 2D grid is an element that is strictly greater than all of its adjacent neighbors to the left, right, top, and bottom.
+ * Given a 0-indexed m x n matrix mat where no two adjacent cells are equal, find any peak element mat[i][j] and return the length 2 array [i,j].
+ * You may assume that the entire matrix is surrounded by an outer perimeter with the value -1 in each cell.
+ * You must write an algorithm that runs in O(m log(n)) or O(n log(m)) time.
+ *  
+ * Example 1:
+ * <img alt="" src="https://assets.leetcode.com/uploads/2021/06/08/1.png" style="width: 206px; height: 209px;" />
+ *
+ * Input: mat = [[1,4],[3,2]]
+ * Output: [0,1]
+ * Explanation: Both 3 and 4 are peak elements so [1,0] and [0,1] are both acceptable answers.
+ *
+ * Example 2:
+ * <img alt="" src="https://assets.leetcode.com/uploads/2021/06/07/3.png" style="width: 254px; height: 257px;" />
+ *
+ * Input: mat = [[10,20,15],[21,30,14],[7,16,32]]
+ * Output: [1,1]
+ * Explanation: Both 30 and 32 are peak elements so [1,1] and [2,2] are both acceptable answers.
+ *
+ *  
+ * Constraints:
+ *
+ * 	m == mat.length
+ * 	n == mat[i].length
+ * 	1 <= m, n <= 500
+ * 	1 <= mat[i][j] <= 10^5
+ * 	No two adjacent cells are equal.
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/find-a-peak-element-ii/
+// discuss: https://leetcode.com/problems/find-a-peak-element-ii/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    pub fn find_peak_grid(mat: Vec<Vec<i32>>) -> Vec<i32> {
+        let mut start = 0_usize;
+        let mut end = mat.len();
+
+        let (m, n) = (mat.len(), mat[0].len());
+
+        while start < end {
+            let mid: usize = (start + end) / 2;
+            let (mut max_idx, mut max_val) = (0_usize, mat[mid][0]);
+
+            for i in 0..n {
+                if mat[mid][i] > max_val {
+                    max_idx = i;
+                    max_val = mat[mid][i];
+                }
+            }
+
+            if mid > 0 && mat[mid - 1][max_idx] > max_val {
+                end = mid;
+            } else if mid < m - 1 && mat[mid + 1][max_idx] > max_val {
+                start = mid + 1;
+            } else {
+                return vec![mid as i32, max_idx as i32];
+            }
+        }
+
+        vec![0, 0]
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[ignore]
+    fn test_1901_example_1() {
+        let mat = vec![vec![1, 4], vec![3, 2]];
+
+        let result = vec![0, 1];
+
+        assert_eq!(Solution::find_peak_grid(mat), result);
+    }
+
+    #[test]
+    #[ignore]
+    fn test_1901_example_2() {
+        let mat = vec![vec![10, 20, 15], vec![21, 30, 14], vec![7, 16, 32]];
+
+        let result = vec![1, 1];
+
+        assert_eq!(Solution::find_peak_grid(mat), result);
+    }
+}