轮询

class Solution {
public:
    int GetNumberOfK(vector<int> data ,int k) {
        if (data.empty()) return 0;
        int cnt = 0; 
        for (int i = 0; i < data.size(); ++i) {
            if (k == data[i]) {
                cnt++;
            }
        }
        return cnt;
    }
};

二分

#include <vector>
class Solution {
public:
    int GetNumberOfK(vector<int> data ,int k) {
        if (data.empty()) return 0;
        int cnt = 0; 
        int left_idx = getLeftRange(data, k);
        int right_idx = getRightRange(data, k);
        return right_idx - left_idx + 1;
    }

    int getLeftRange(vector<int>& data, int k) {
        int l = 0;
        int r = data.size() - 1;
        while (l <= r) {
            int mid = l + (r - l) / 2;
            if (data[mid] >= k) {
                r = mid - 1;
            } else if (data[mid] < k) {
                l = mid + 1;
            }
        }
        return l;
    }

    int getRightRange(vector<int>& data, int k) {
        int l = 0;
        int r = data.size() - 1;
        while (l <= r) {
            int mid = l + (r - l) / 2;
            if (data[mid] > k) {
                r = mid - 1;
            } else if (data[mid] <= k) {
                l = mid + 1;
            }
        }
        return r;
    }
};