二分查找的过程

对于已经排好序的序列，查找某个值的下标，采用二分查找法

    public static int getIndex(int[] a,int x) {
        int start = 0;
        int end = a.length-1;
        while (start<=end) {
            int middle = (end+start)/2;
            if(x==a[middle]) 
                return middle;
            else if (x<a[middle]) {
                end = middle -1;
            }else {
                start = middle +1;
            }
        }   
        return -1;  
    }