# Matrix Problem : Find the number of persons seen

1 min readAug 17, 2022

Given a grid G of numbers representing heights of persons standing next to each other.

- A person can see another person in the grid if the height of everyone in between is shorter than them
- A person can see to the right and down

Return a grid A where A[x][y] is the sum of all the persons seen from G[x][y]

Example

[9, 6, 8, 5, 11]

[1, 5, 3, 7, 9]

[2, 1, 4, 6, 1]

Output

[5, 3, 4, 2, 1]

[4, 4, 3, 2, 1]

[3, 2, 1, 1, 0]

For example:`In last row:`

`For :[2, 1, 4, 6, 1] `

for 2: [1, 4, 6] = 3

for 1: [4, 6] = 2

for 4: [6] = 1

for 6: [1] = 1

for 1: [] = 0

Idea: Going to use monotonic stack to solve this problem