37、数字在排序数组中出现的次数

一、题目

统计一个数字在排序数组中出现的次数。

二、解法

public class Solution {
   public int GetNumberOfK(int [] array , int k) {
        if(array == null || array.length == 0)
            return 0;
        int first = GetFirst(array,k,0,array.length-1);
        int last = GetLast(array,k,0,array.length-1);
        if(first == -1 || last == -1)
            return 0;
        return last-first+1;
    }
    //获取第一个
    public int GetFirst(int[] array,int k, int start, int end){
        while(start <= end){
            int mid = (start+end)/2;
           if(k < array[mid])
               end = mid-1;
           else if(k > array[mid])
               start = mid+1;
           else{//当相等的时候 并左边一个不等于k 或者是第一个
               if(mid == 0 || (mid > 0 && array[mid-1] != k))
                   return mid;
               else
                   end = mid-1;
           }
        }
        return -1;
    }
    //获取最后一个
    public int GetLast(int[] array,int k, int start, int end){
        while(start<=end){
            int mid = (start+end)/2;
            if(k < array[mid])
                end = mid-1;
            else if(k > array[mid])
                start = mid+1;
            else{
                //当相等的时候，下标等于最后一个 或者右边一个不等于k
                if(mid == array.length-1 || 
                  (mid < array.length-1 && array[mid+1] != k))
                    return mid;
                else
                    start = mid+1;
            }
        }
        return -1;
    }
}