How to store multiple 2D array locations in C? - c

Question

I'm trying to make a simple program, that generates random numbers into a 15x15 2D array and then works with the array later on.
This function finds the largest value in the array and then prints out the value and its location.
void maxValue(int array[ROWS][COLUMNS]){
int maxNum = array[0][0];
int rowMaxLocation;
int columnMaxLocation;
for(int c = 0; c < ROWS; c++) {
for(int d = 0; d < COLUMNS; d++) {
if(maxNum < array[c][d]) {
maxNum = array[c][d];
rowMaxLocation = c;
columnMaxLocation = d;
}
}
}
printf("Largest value in the array is %d, located in [%d][%d]", maxNum, rowMaxLocation, columnMaxLocation);
return;
What I can't figure out is how to store multiple locations of the same maximal value, e.g. "Largest value in the array is 99, located in [1][3] and [5][12]".
Thanks in advance.

Answer 1

you can follow a two pass approach:
First pass: Find maximum element in array
Second pass: Find all indices where array value is equal to maximum element
In order to store multiple locations you can have arrays of rowMaxLocations[] or columnMaxLocations[] and store values in them accordingly as you scan the array during second pass. If you don't need these values, you can simply skip storing them in some array and just do printing in second pass as well.
I would recommend having a Location struct for storing location values like this:
typedef struct Location {
int row;
int column;
} Location;
Here is how this two pass approach would look like:
void maxValue(int array[ROWS][COLUMNS]){
int maxNum = array[0][0];
// Array of locations to store max locations
Location maxLocations[ROWS * COLUMNS];
// Index of max locations array
int maxLocationIndex = 0;
// First pass; Get Max value
for(int c = 0; c < ROWS; c++) {
for(int d = 0; d < COLUMNS; d++) {
if(maxNum < array[c][d]) {
maxNum = array[c][d];
}
}
}
// Seconds pass; Get all values equal to max value
for (int c = 0; c < ROWS; c++) {
for (int d = 0; d < COLUMNS; d++) {
if (array[c][d] == maxNum) {
maxLocations[maxLocationIndex].row = c;
maxLocations[maxLocationIndex].column = d;
maxLocationIndex++;
}
}
}
// Print the max locations array
printf("Largest value in the array is %d\n", maxNum);
for (int i = 0; i < maxLocationIndex; i++) {
printf("[%d][%d] \n", maxLocations[i].row, maxLocations[i].column);
}
}
Update:
Thanks to suggestion from #Ian Abbott, there is also a way to do all this in one pass. We would just need to reset the maxLocationIndex whenever we find a new max value:
for(int c = 0; c < ROWS; c++) {
for(int d = 0; d < COLUMNS; d++) {
if(maxNum < array[c][d]) {
maxNum = array[c][d];
// Reset Max locations index
maxLocationIndex = 0;
}
if (array[c][d] == maxNum) {
maxLocations[maxLocationIndex].row = c;
maxLocations[maxLocationIndex].column = d;
maxLocationIndex++;
}
}
}