题解 | #数字在升序数组中出现的次数#

二分法查找，

public class Solution {
    public int GetNumberOfK(int [] array , int k) {
        if(array==null ||array.length==0) return 0;
        if(k<array[0]||k>array[array.length-1]) return 0;
       int left=0,right=array.length-1;
        int count=0,mid=0;
        while(left<=right){
            mid =(left+right)/2;
            if(array[mid]>k) right=mid-1;
            else if(array[mid]<k) left=mid+1;
            else{//相等
                count++;
                break;
            }
        }
        left=mid-1;
        right=mid+1;
        while(left>=0 && array[left]==k ) {
            count++;
            left--;
        }
        while( right<array.length && array[right]==k) {
            count++;
            right++;
        }
        return count;
    }
}