for each cell, compute the longest streak of 1s in four directions: left, right, up, down. use separate passes for each direction to build these counts efficiently.
the order of a plus sign centered at a cell is the minimum of all four directional streaks. find the maximum order across all cells.
approach
- build four 2d arrays for left, right, up, down streaks
- for each direction, do a single pass to compute streaks
- for each cell, take min of four directions as plus order
- track the maximum order found
complexity
O(n²) time for four passes over the grid, O(n²) space for the four direction arrays. efficient dp solution.