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Longest Border-Ending Diagonal Pattern

Duolingo● MediumNEW GRADOA

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Problem statement

Given a rectangular integer matrix matrix, find the longest diagonal segment that matches the infinite pattern 1, 2, 0, 2, 0, ....

A valid segment:

starts at any matrix cell whose value is 1;
continues in exactly one of the four diagonal directions;
matches 2 after the initial 1, then alternates 0 and 2; and
ends at a cell on the first row, last row, first column, or last column.

Return the maximum length of a valid segment.

Function

longestBorderDiagonal(matrix: int[][]) → int

Examples

Example 1

matrix = [[0,0,1,2],[0,2,2,2],[2,1,0,1]]return = 3

Starting at matrix[2][3] and moving up-left produces 1, 2, 0 at cells (2,3), (1,2), and (0,1). The last cell is on the first row, so this is a valid length-3 segment. No longer valid segment exists.

Constraints

matrix is non-empty and rectangular.
Every matrix value is 0, 1, or 2.
A segment moves by one row and one column at each step and never changes direction.
A solution with time complexity no worse than O(matrix.length^2 * matrix[0].length^2) fits the source's execution limit.