How should I practice Count Starts Reaching a Grid Maximum?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Duolingo phone screen problems in FastPrep.

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FastPrep tags this as a Duolingo phone screen coding practice problem when the problem catalog has that company and stage context.

Count Starts Reaching a Grid Maximum

Duolingo● MediumINTERNPHONE SCREEN

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Problem statement

You are given a rectangular height matrix. From a cell, inspect all eight neighboring cells and move to the strictly higher neighbor with greatest height. If several eligible neighbors have that height, choose the one with smaller row, then smaller column. Stop when no higher neighbor exists.

Return the number of starting cells whose path ends at any cell whose value equals the global maximum of the matrix.

Function

countStartsReachingMaximum(heights: int[][]) → int

Examples

Example 1

heights = [[1,2],[3,4]]return = 4

Every cell moves directly or indirectly to the global maximum 4.

Example 2

heights = [[9,1,8],[1,7,1],[6,1,5]]return = 7

Seven starts reach 9; the cell 8 and the adjacent 1 that chooses it stop at the non-global local maximum.

Constraints

1 <= heights.length, heights[0].length
heights.length * heights[0].length <= 200000
-1000000000 <= heights[r][c] <= 1000000000
All rows have equal length.