'Surrounded Regions' soln

Author: joewnga

leetcode/surrounded_regions.rs

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+/// 
+/// Problem: Surrounded Regions
+/// 
+/// Given an m x n matrix board containing 'X' and 'O', capture all regions that are 4-directionally 
+/// surrounded by 'X'.
+/// 
+/// A region is captured by flipping all 'O's into 'X's in that surrounded region.
+/// 
+/// Example 1:
+/// Input: board = [["X","X","X","X"],["X","O","O","X"],["X","X","O","X"],["X","O","X","X"]]
+/// Output: [["X","X","X","X"],["X","X","X","X"],["X","X","X","X"],["X","O","X","X"]]
+/// Explanation: Notice that an 'O' should not be flipped if:
+/// - It is on the border, or
+/// - It is adjacent to an 'O' that should not be flipped.
+/// The bottom 'O' is on the border, so it is not flipped.
+/// The other three 'O' form a surrounded region, so they are flipped.
+/// 
+/// Example 2:
+/// Input: board = [["X"]]
+/// Output: [["X"]]
+/// 
+/// Constraints:
+/// m == board.length
+/// n == board[i].length
+/// 1 <= m, n <= 200
+/// board[i][j] is 'X' or 'O'.
+/// 
+
+// # Solution
+// Time complexity: O(m*n) 
+// Space complexity: O(m*n)
+
+impl Solution {
+    pub fn solve(board: &mut Vec<Vec<char>>) {
+        if board.is_empty() || board[0].is_empty() {
+           return;
+       }
+       
+       let rows = board.len();
+       let cols = board[0].len();
+       
+       
+       for col in 0..cols {
+           Self::dfs(board, 0, col as i32, rows as i32, cols as i32);
+           Self::dfs(board, (rows - 1) as i32, col as i32, rows as i32, cols as i32);
+       }
+       
+       for row in 0..rows {
+           Self::dfs(board, row as i32, 0, rows as i32, cols as i32);
+           Self::dfs(board, row as i32, (cols - 1) as i32, rows as i32, cols as i32);
+       }
+       
+       for row in 0..rows {
+           for col in 0..cols {
+               if board[row][col] == 'O' {
+                   board[row][col] = 'X'; 
+               } else if board[row][col] == 'E' {
+                   board[row][col] = 'O'; 
+               }
+           }
+       }
+   }
+   
+   fn dfs(board: &mut Vec<Vec<char>>, row: i32, col: i32, rows: i32, cols: i32) {
+       if row < 0 || row >= rows || col < 0 || col >= cols || board[row as usize][col as usize] != 'O' {
+           return;
+       }
+       
+       board[row as usize][col as usize] = 'E';
+       
+       Self::dfs(board, row + 1, col, rows, cols);
+       Self::dfs(board, row - 1, col, rows, cols);
+       Self::dfs(board, row, col + 1, rows, cols);
+       Self::dfs(board, row, col - 1, rows, cols);
+    }
+}