题解 | 数字在升序数组中出现的次数

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param nums int整型vector 
     * @param k int整型 
     * @return int整型
     */
    int GetLeftMostPos(const vector<int>& nums, int k) {
        int m = nums.size();
        int left = 0;
        int right = m - 1;

        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] >= k) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }

        return (left < m && nums[left] == k) ? left : -1;
    }
    int GetRightMostPos(const vector<int>& nums, int k) {
        int m = nums.size();
        int left = 0;
        int right = m - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] <= k) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        return (right >= 0 && nums[right] == k) ? right : -1;
    }
    int GetNumberOfK(vector<int>& nums, int k) {
        // write code here
        int leftMost = GetLeftMostPos(nums, k);
        int rightMost = GetRightMostPos(nums, k);
        return rightMost >= leftMost && leftMost >= 0 ? 
                (rightMost - leftMost + 1) : 0;
    }
};