1568. Minimum Number of Days to Disconnect Island: RETRY, credit: https://leetcode.com/problems/minimum-number-of-days-to-disconnect-island/solutions/3171061/just-a-runnable-solution/

Author: tan-wei

src/solution/mod.rs

@@ -1182,3 +1182,4 @@ mod s1562_find_latest_group_of_size_m;
 mod s1563_stone_game_v;
 mod s1566_detect_pattern_of_length_m_repeated_k_or_more_times;
 mod s1567_maximum_length_of_subarray_with_positive_product;
+mod s1568_minimum_number_of_days_to_disconnect_island;

src/solution/s1568_minimum_number_of_days_to_disconnect_island.rs

@@ -0,0 +1,123 @@
+/**
+ * [1568] Minimum Number of Days to Disconnect Island
+ *
+ * You are given an m x n binary grid grid where 1 represents land and 0 represents water. An island is a maximal 4-directionally (horizontal or vertical) connected group of 1's.
+ * The grid is said to be connected if we have exactly one island, otherwise is said disconnected.
+ * In one day, we are allowed to change any single land cell (1) into a water cell (0).
+ * Return the minimum number of days to disconnect the grid.
+ *  
+ * Example 1:
+ * <img alt="" src="https://assets.leetcode.com/uploads/2021/12/24/land1.jpg" style="width: 500px; height: 169px;" />
+ * Input: grid = [[0,1,1,0],[0,1,1,0],[0,0,0,0]]
+ * Output: 2
+ * Explanation: We need at least 2 days to get a disconnected grid.
+ * Change land grid[1][1] and grid[0][2] to water and get 2 disconnected island.
+ *
+ * Example 2:
+ * <img alt="" src="https://assets.leetcode.com/uploads/2021/12/24/land2.jpg" style="width: 404px; height: 85px;" />
+ * Input: grid = [[1,1]]
+ * Output: 2
+ * Explanation: Grid of full water is also disconnected ([[1,1]] -> [[0,0]]), 0 islands.
+ *
+ *  
+ * Constraints:
+ *
+ * 	m == grid.length
+ * 	n == grid[i].length
+ * 	1 <= m, n <= 30
+ * 	grid[i][j] is either 0 or 1.
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/minimum-number-of-days-to-disconnect-island/
+// discuss: https://leetcode.com/problems/minimum-number-of-days-to-disconnect-island/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    // Credit: https://leetcode.com/problems/minimum-number-of-days-to-disconnect-island/solutions/3171061/just-a-runnable-solution/
+    pub fn min_days(grid: Vec<Vec<i32>>) -> i32 {
+        let mut grid = grid;
+        let mut islands = Self::count_islands(&grid);
+        let (n, m) = (grid.len(), grid[0].len());
+        if islands > 1 || islands == 0 {
+            return 0;
+        }
+
+        for i in 0..n {
+            for j in 0..m {
+                if grid[i][j] == 1 {
+                    grid[i][j] = 0;
+                    islands = Self::count_islands(&grid);
+                    grid[i][j] = 1;
+                    if islands > 1 || islands == 0 {
+                        return 1;
+                    }
+                }
+            }
+        }
+
+        2
+    }
+
+    fn dfs_helper(x: usize, y: usize, grid: &Vec<Vec<i32>>, vis: &mut Vec<Vec<i32>>) {
+        let dx = vec![1, -1, 0, 0];
+        let dy = vec![0, 0, 1, -1];
+        let (n, m) = (grid.len(), grid[0].len());
+        vis[x][y] = 1;
+        for a in 0..4 {
+            let nx = x as i32 + dx[a];
+            let ny = y as i32 + dy[a];
+            if nx >= 0
+                && ny >= 0
+                && nx < n as i32
+                && ny < m as i32
+                && vis[nx as usize][ny as usize] == 0
+                && grid[nx as usize][ny as usize] == 1
+            {
+                Self::dfs_helper(nx as usize, ny as usize, grid, vis);
+            }
+        }
+    }
+
+    fn count_islands(grid: &Vec<Vec<i32>>) -> i32 {
+        let mut islands = 0;
+        let (n, m) = (grid.len(), grid[0].len());
+        let mut vis = vec![vec![0; m]; n];
+        for i in 0..n {
+            for j in 0..m {
+                if vis[i][j] == 0 && grid[i][j] == 1 {
+                    Self::dfs_helper(i, j, grid, &mut vis);
+                    islands += 1;
+                }
+            }
+        }
+        islands
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1568_example_1() {
+        let grid = vec![vec![0, 1, 1, 0], vec![0, 1, 1, 0], vec![0, 0, 0, 0]];
+
+        let result = 2;
+
+        assert_eq!(Solution::min_days(grid), result);
+    }
+
+    #[test]
+    fn test_1568_example_2() {
+        let grid = vec![vec![1, 1]];
+
+        let result = 2;
+
+        assert_eq!(Solution::min_days(grid), result);
+    }
+}