Question

I have a large array. I have some Java code for identifying indices for start and end points for a subset/slice of that large array. The only information items that I need to retrieve from the selected subsection of the array are the indices and values of the local maximum and minimum. What is the fastest (and least memory intensive) way that I can find a max and min within the specified range?

Here is a start of what I need in terms of code:

// Step One: declare new array and populate it
pts = new double[5000];
for (int i = 0; i < 5000; i++){ pts[i] = (value assigned by extraneous process);}
// Step Two: slice out section between indices 3600 and 3750
    // what code do I write here?
// Step Three: find max value in the sliced section and return its index
    // what code to I write here?

Answer 1

Just iterate over the desired range and record maximum and minimum seen values:

double max = Double.NEGATIVE_INFINITY;
double min = Double.POSITIVE_INFINITY;
int minIndex = -1;
int maxIndex = -1;
for(int k = 3600; k < 3750; k++){
    if(max < pts[k]){
        max = pts[k];
        maxIndex = k;
    }else if(min > pts[k]){
        min = pts[k];
        minIndex = k;
    }
}