如果要找大于等于target的第一个数:

public int binarySearch (int[] nums, int target) {
    if(nums.length == 0) return 0;
    int left = 0, right = nums.length - 1;
    while(left < right){
        int mid = left + right >> 1;
        if(nums[mid] >= target) right = mid;
        else left = mid + 1;
    }
    return right;
}

如果要找小于等于target的最后一个数:

public int binarySearch (int[] nums, int target) {
    if(nums.length == 0) return 0;
    int left = 0, right = nums.length - 1;
    while(left < right){
        int mid = left + right + 1>> 1;
        if(nums[mid] <= target) left = mid;
        else right = mid - 1;
    }
    return left;
}