1var latestDayToCross = function(row, col, cells) {
2    const directions = [[0, 1], [1, 0], [0, -1], [-1, 0]];
3    let grid, r, c;
4
5    const isValid = (x, y) => {
6        return x >= 0 && x < r && y >= 0 && y < c && grid[x][y] === 0;
7    };
8
9    const dfs = (x, y) => {
10        if (x === r - 1) return true;
11        grid[x][y] = 1;
12        for (const [dx, dy] of directions) {
13            const nx = x + dx, ny = y + dy;
14            if (isValid(nx, ny) && dfs(nx, ny)) return true;
15        }
16        return false;
17    };
18
19    const canCross = (day) => {
20        grid = Array.from({ length: row }, () => Array(col).fill(0));
21        for (let i = 0; i <= day; i++) {
22            grid[cells[i][0] - 1][cells[i][1] - 1] = 1;
23        }
24        for (let i = 0; i < col; i++) {
25            if (grid[0][i] === 0 && dfs(0, i)) return true;
26        }
27        return false;
28    };
29
30    let left = 0, right = cells.length - 1, lastValidDay = 0;
31    while (left <= right) {
32        const mid = left + Math.floor((right - left) / 2);
33        if (canCross(mid)) {
34            lastValidDay = mid;
35            left = mid + 1;
36        } else {
37            right = mid - 1;
38        }
39    }
40    return lastValidDay + 1;
41};