https://leetcode.com/problems/surrounded-regions

surrounded-regions.js

const O = 'O';
const X = 'X';
const T = 'T';

/**
 * @param {character[][]} board
 * @return {void} Do not return anything, modify board in-place instead.
 */
var solve = function(board) {
    if (board.length < 2 || board[0].length < 2) {
        return;
    }
    
    for (let [x, y] of findBoundaryZeros(board)) {
        fillZeroRegion(board, x, y);
    }
    
    for (let y = 0; y < board.length; y++) {
        for (let x = 0; x < board[0].length; x++) {
            const value = board[y][x];
            
            if (value === X) {
                continue;
            }
            
            if (value === T) {
                board[y][x] = O;
                continue;
            }
            
            board[y][x] = X;
        }
    }
};

function findBoundaryZeros(board) {
    const result = [];
    const yMin = 0;
    const yMax = board.length - 1;
    const xMin = 0;
    const xMax = board[0].length - 1;
    
    for (let x = 0; x <= xMax; x++) {
        if (board[yMin][x] === O) {
            result.push([x, yMin]);
        }
        
        if (board[yMax][x] === O) {
            result.push([x, yMax]);
        }
    }
    
    for (let y = 0; y <= yMax; y++) {
        if (board[y][xMin] === O) {
            result.push([xMin, y]);
        }
        
        if (board[y][xMax] === O) {
            result.push([xMax, y]);
        }
    }
    
    return result;
}

function fillZeroRegion(board, x, y) {
    if (!checkBoundaries(board, x, y)) {
        return;
    }
    
    if (board[y][x] !== O) {
        return;
    }
    
    board[y][x] = T;
    fillZeroRegion(board, x - 1, y);
    fillZeroRegion(board, x + 1, y);
    fillZeroRegion(board, x, y - 1);
    fillZeroRegion(board, x, y + 1);
}

function checkBoundaries(board, x, y) {
    if (y < 0 || y >= board.length) {
        return false;
    }
    
    if (x < 0 || x >= board[0].length) {
        return false;
    }
    
    return true;
}