So this method is passed an arraylist of Occurences, which each contain a string and a frequency. The frequency is the only important part here. But what I need to do is use binary search to insert the last element in the arraylist into the sorted position. Every time I run this code, the insertion position is printed as -1. Am I missing something in my code?
I need to keep track of the indexes in the array I hit during binary search, which shouldn't be too difficult, but explains the return type.
public ArrayList<Integer> insertLastOccurrence(ArrayList<Occurrence> occs) {
ArrayList<Integer> path = new ArrayList<Integer>();
int targetFreq = occs.get(occs.size()-1).frequency; //gets the frequency of the thing we want to insert
//if the array is just 1 value, don't do anything
if(occs.size() == 1){
return null;
}
int start = 0; // The start of the search region
int end = occs.size()-2;// The end of the search region is 1 less than the last position
int position = -1; // Position of the target
// While there is still something list left to search and
// the element has not been found
while (start <= end && position == -1) {
int mid = start + (end - start) / 2; //int mid = (start + end) / 2; // Location of the middle
// Determine whether the target is smaller than, greater than,
// or equal to the middle element
if (targetFreq < occs.get(mid).frequency) {
// Target is smaller; continue the left half
end = mid - 1;
}
else if (targetFreq > occs.get(mid).frequency) {
// Target is larger, continue the right half
start = mid + 1;
}
else {
// Found it!
position = mid;
}
}
System.out.println(position);
return path;
}
