Problem 319. Biggest Value in the (Neighbor)Hood

Created by Hans

Solve Later

For this challenge you get two inputs: a matrix A and an integer value n. Your function should return a Matrix B of the same size as A with integer values. Thereby, the entry B(i,j) counts the occurrence of lower values in the neighborhood A(i-n:i+n,j) (column wise), while symmetric boundary conditions (A(i<1,j) == A(-i+1,j) should be used (compare to padarray('symmetric')). For example,
assume n to be 2 and a matrix A containing double values, e.g.
A =
    0.3147   -0.4025   -0.3424   -0.3581    0.1557    0.2577    0.2060
    0.4058   -0.2215    0.4706   -0.0782   -0.4643    0.2431   -0.4682
   -0.3730    0.0469    0.4572    0.4157    0.3491   -0.1078   -0.2231
    0.4134    0.4575   -0.0146    0.2922    0.4340    0.1555   -0.4538
    0.1324    0.4649    0.3003    0.4595    0.1787   -0.3288   -0.4029
then, your function should return
B =
     2     1     1     1     3     4     4
     3     2     4     2     0     2     0
     0     2     3     3     3     1     3
     4     2     0     1     4     3     1
     2     4     3     4     1     1     3
Explanation: Consider the value -0.3730 in the first column of A. The two entries above and below are all bigger and thus, the corresponding entry in B is 0. However, the entry 0.4134 is bigger than its neighbors (symmetric boundary condition) and thus, the corresponding entry in B is 4. You can assume that n<=size(A,1)

Solve

Solution Stats

96 Solutions
26 Solvers

Last Solution submitted on Jan 02, 2026

Last 200 Solutions

Problem Comments

6 Comments

6 Comments

Show 3 older comments

Venu Lolla on 14 Feb 2012

Is the B matrix described above correct?

Alfonso Nieto-Castanon on 15 Feb 2012

no, I believe the first and last rows should read [1 0 0 0 2 3 3] and [1 3 2 3 0 0 2], respectively

rifat on 5 Feb 2015

Is the test suite correct now? An old problem though...

Jan Orwat on 5 Feb 2015

Hello Rifat, I've solved this one recently, and it seems to be ok.

Dyuman Joshi on 21 Feb 2023

The test suite has been updated and solutions have been rescored.

George Berken on 2 Jan 2026 at 12:35

The example given above is incorrect for B.
See Case Test 1 for the correct B example.
B = [1 0 0 0 2 3 3;...
3 2 4 2 0 2 0;...
0 2 3 3 3 1 3;...
4 2 0 1 4 3 1;...
1 3 2 3 0 0 2]

Solution Comments

Show comments

Problem Recent Solvers26

Problem Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!