数组中查找数字出现的次数（二分法）

统计一个数字在排序数组中出现的次数。

示例 1:

输入: nums = [5,7,7,8,8,10], target = 8 输出: 2

 // 左边界
    public static int searchLeft(int[] arr,int k){
        int l = 0;
        int r = arr.length-1;
        while (l<r){
            int mid = (l+r)>>1;
            if(arr[mid] == k){
                r = mid;
            }else if(arr[mid]>k){
                r = mid-1;
            }else {
                l = mid+1;
            }
        }
        return r;

    }
    // 右边界
    public static int searchRight(int[] arr,int k){
        int l = 0;
        int r = arr.length-1;
        while (l<r){
            // 每次计算取前一位整，这里加一取后一位，避免死循环
            int mid = (l+r+1)>>1;
            if(arr[mid] == k){
                l = mid;
            }else if(arr[mid]>k){
                r = mid-1;
            }else {
                l = mid+1;
            }
        }
        return l;

    }
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