From ad01cb36900445217a038f67869265af91ab5f9e Mon Sep 17 00:00:00 2001
From: Dale Seo <5466341+DaleSeo@users.noreply.github.com>
Date: Sat, 8 Aug 2026 12:08:04 -0400
Subject: [PATCH] number-of-islands

---
 number-of-islands/DaleSeo.rs | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 number-of-islands/DaleSeo.rs

diff --git a/number-of-islands/DaleSeo.rs b/number-of-islands/DaleSeo.rs
new file mode 100644
index 0000000000..cf12f80805
--- /dev/null
+++ b/number-of-islands/DaleSeo.rs
@@ -0,0 +1,34 @@
+// TC: O(m * n)
+// SC: O(m * n)
+impl Solution {
+    pub fn num_islands(mut grid: Vec<Vec<char>>) -> i32 {
+        let mut cnt = 0;
+        for r in 0..grid.len() {
+            for c in 0..grid[r].len() {
+                if grid[r][c] == '1' {
+                    cnt += 1;
+                    Self::sink(&mut grid, r, c);
+                }
+            }
+        }
+        cnt
+    }
+
+    fn sink(grid: &mut Vec<Vec<char>>, row: usize, col: usize) {
+        grid[row][col] = '0';
+        let mut stack = vec![(row, col)];
+        while let Some((row, col)) = stack.pop() {
+            for (r, c) in [
+                (row, col.wrapping_sub(1)),
+                (row, col + 1),
+                (row.wrapping_sub(1), col),
+                (row + 1, col),
+            ] {
+                if r < grid.len() && c < grid[r].len() && grid[r][c] == '1' {
+                    grid[r][c] = '0';
+                    stack.push((r, c));
+                }
+            }
+        }
+    }
+}