How should I practice Maximum Rocks on a North-or-East Grid Path?

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

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Problem · Array

Maximum Rocks on a North-or-East Grid Path

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Goldman SachsFULLTIMEPHONE SCREEN

Problem statement

You are given a rectangular grid rocks, where rocks[row][column] is the number of rocks available in one city. Rows are ordered from south to north, and columns are ordered from west to east.

Start at the southwestern city [0, 0] and finish at the northeastern city [rows - 1, columns - 1]. From each city, you may move one row north or one column east.

Collect all rocks in every visited city, including the start and destination. Return the maximum number of rocks that can be collected.

Function

maximumCollectedRocks(rocks: int[][]) → long

Examples

Example 1

rocks = [[5,1,2],[2,10,1],[1,1,20]]return = 38

One optimal path visits values 5, 2, 10, 1, 20, for a total of 38.

Example 2

rocks = [[4,2,7]]return = 13

With one row, the only path moves east through all three cities and collects 4 + 2 + 7 = 13.

Constraints

1 <= rocks.length <= 500
1 <= rocks[row].length <= 500
Every row has the same length.
0 <= rocks[row][column] <= 10^9
The result fits in a signed 64-bit integer.