Java O(m*n) DP with O(n) space


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    public class Solution {
        public int longestLine(int[][] M) {
            
            int m = M.length, ones = 0;
            if (m > 0) {
                int n = M[0].length;
                int[][] old = new int[4][n];
                for (int i = 0; i < m; i++) {
                    int[][] curr = new int[4][n];
                    for (int j = 0; j < n; j++) {
                        if (M[i][j] == 1) {
                            curr[0][j] = ((j > 0) ? curr[0][j - 1] + 1 : 1);
                            curr[1][j] = ((i > 0) ? old[1][j] + 1 : 1);
                            curr[2][j] = ((j < n - 1) ? old[2][j + 1] + 1 : 1);
                            curr[3][j] = ((j > 0) ? old[3][j - 1] + 1 : 1);
                            ones = Math.max(ones, Math.max(Math.max(curr[0][j], curr[1][j]), Math.max(curr[2][j], curr[3][j])));
                        } else {
                            curr[0][j] = curr[1][j] = curr[2][j] = curr[3][j] = 0;
                        }
                    }
                    
                    old = curr;
                }
            }
            
            return ones;
        }
    }
    

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