286 Walls and Gates.js

// You are given a m x n 2D grid initialized with these three possible values.

// -1 - A wall or an obstacle.
// 0 - A gate.
// INF - Infinity means an empty room. We use the value 231 - 1 = 2147483647 to represent INF as you may assume that the distance to a gate is less than 2147483647.
// Fill each empty room with the distance to its nearest gate. If it is impossible to reach a gate, it should be filled with INF.

// For example, given the 2D grid:
// INF  -1  0  INF
// INF INF INF  -1
// INF  -1 INF  -1
//   0  -1 INF INF
// After running your function, the 2D grid should be:
//   3  -1   0   1
//   2   2   1  -1
//   1  -1   2  -1
//   0  -1   3   4
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var wallsAndGates = function(rooms) {
    var gates = [];
    
    if(!rooms || rooms.length === 0) {
        return;
    }
    
    var rows = rooms.length;
    var cols = rooms[0].length;
    
    
    for(var i = 0; i < rows; i++) {
        for(var j = 0; j < cols; j++) {
            // find all gates
            if(rooms[i][j] === 0) {
                traverse(rooms, i, j, rows, cols, 0);
            }
        }
    }
};

function traverse(rooms, i, j, rows, cols, dist) {
    if(i >= 0 && i < rows && j >= 0 && j < cols) {
        if(rooms[i][j] !== -1 && rooms[i][j] >= dist) {
            rooms[i][j] = dist;
            traverse(rooms, i + 1, j, rows, cols, dist + 1);
            traverse(rooms, i, j + 1, rows, cols, dist + 1);
            traverse(rooms, i - 1, j, rows, cols, dist + 1);
            traverse(rooms, i, j - 1, rows, cols, dist + 1);
        }
    }
}




// second attempt

/**
 * @param {number[][]} rooms
 * @return {void} Do not return anything, modify rooms in-place instead.
 */
var wallsAndGates = function(rooms) {
    for(var i = 0; i < rooms.length; i++) {
        for(var j = 0; j < rooms[i].length; j++) {
            if(rooms[i][j] === 0) {
                dfs(rooms, i, j, 0);
            }
        }
    }
    
    function dfs(rooms, i, j, dist) {
        if(i >= 0 && i < rooms.length && j >= 0 && j < rooms[i].length) {
        
            if(rooms[i][j] === -1 || rooms[i][j] < dist) {
                return;
            }
            
            if(rooms[i][j] > dist) {
               rooms[i][j] = dist; 
            }
            
            dfs(rooms, i + 1, j, dist + 1);
            dfs(rooms, i - 1, j, dist + 1);
            dfs(rooms, i, j + 1, dist + 1);
            dfs(rooms, i, j - 1, dist + 1);
        }
    }
};