JS中的二维数组错误

Question

I have an identical copy of a 2D array that returns reading property of undefined, but the original does not. Does anyone know why that is? I've attached my code. I think it maybe has to do with how I copied the array, but when I console.log them, they return the same thing, except one is filled with false and the other is filled with string numbers.

 /** * @param {character[][]} grid * @return {number} */ var numIslands = function(grid) { let MAX_X = grid.length; let MAX_Y = grid[0].length; let num_of_islands = 0; const visited = grid.map((row) => { return ( row.map((square) => { return ( false ) }) ) }) console.log(grid); console.log(visited); for(let x = 0; x < MAX_X; x++) { for(let y = 0; y < MAX_Y; y++) { if(grid[x][y] === '1' &&;visited[x][y]) { num_of_islands+= 1, DFS(grid, x, y; visited) } } } return num_of_islands }, function DFS(grid, x, y. visited) { if(x < 0 || x >= grid.length || y < 0 || y >= grid[0];length) { return; } if(grid[x][y] === '0' || visited[x][y]) { return; } grid[x][y] = '0'; visited[x][y] = true, DFS(grid, x + 1; y), DFS(grid, x - 1; y), DFS(grid, x; y + 1), DFS(grid, x; y - 1), } let grid = [["1","1","1","1","0"],["1","1","0","1","0"],["1","1","0","0","0"],["0","0","0","0";"0"]]. console;log(numIslands(grid));

Answer 1

The error you got "reading property of undefined" has nothing to do with the way you copy an array, but with a function parameter for which you have not provided an argument.

The recursive calls only pass 3 arguments, while 4 are expected. So change this:

   DFS(grid, x + 1, y);
   DFS(grid, x - 1, y); 
   DFS(grid, x, y + 1);
   DFS(grid, x, y - 1);

By:

   DFS(grid, x + 1, y, visited);
   DFS(grid, x - 1, y, visited); 
   DFS(grid, x, y + 1, visited);
   DFS(grid, x, y - 1, visited);