面试题_有序数组的二分法解法

剑指 Offer 53 - I. 在排序数组中查找数字 I

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
示例 2:

输入: nums = [5,7,7,8,8,10], target = 6
输出: 0

提示：

0 <= nums.length <= 105
-109 <= nums[i] <= 109
nums 是一个非递减数组
-109 <= target <= 109

代码

class Solution {
public:
    int helper(vector<int>& nums, int target, int left, int right)
    {
        while(left <= right)
        {
            int mid = (left + right) / 2;
            if (nums[mid] <= target) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        return left;
    }
    int search(vector<int>& nums, int target) {
        int nlen = nums.size();

        return helper(nums, target, 0, nlen - 1) - helper(nums, target - 1, 0, nlen - 1);
    }
};