FirstOccurrenceOfNumberInSortedArray.java

package com.interview.binarysearch;

/**
 * http://www.geeksforgeeks.org/check-for-majority-element-in-a-sorted-array/
 */
public class FirstOccurrenceOfNumberInSortedArray {

    public int firstOccurrence(int input[], int x){
        int low = 0;
        int high = input.length-1;
        
        while(low <= high){
            int middle = (low + high)/2;
            if(input[middle] == x && (middle == 0 || input[middle-1] < x)){
                return middle;
            }else if(input[middle] < x){
                low = middle+1;
            }else{
                high = middle-1;
            }
        }
        return -1;
    }
    
    public static void main(String args[]){
        FirstOccurrenceOfNumberInSortedArray fos = new FirstOccurrenceOfNumberInSortedArray();
        int input[] = {1,2,2,2,2,2,5,7,7};
        System.out.println(fos.firstOccurrence(input, 6));
    }
    
}