# 計算排序數組中的出現次數（或頻率） > 原文： [https://www.geeksforgeeks.org/count-number-of-occurrences-or-frequency-in-a-sorted-array/](https://www.geeksforgeeks.org/count-number-of-occurrences-or-frequency-in-a-sorted-array/) 給定一個已排序的數組 arr []和一個數字 x，編寫一個函數計算 arr []中 x 的出現。 預期時間復雜度為 O（Logn） **示例**： ``` Input: arr[] = {1, 1, 2, 2, 2, 2, 3,}, x = 2 Output: 4 // x (or 2) occurs 4 times in arr[] Input: arr[] = {1, 1, 2, 2, 2, 2, 3,}, x = 3 Output: 1 Input: arr[] = {1, 1, 2, 2, 2, 2, 3,}, x = 1 Output: 2 Input: arr[] = {1, 1, 2, 2, 2, 2, 3,}, x = 4 Output: -1 // 4 doesn't occur in arr[] ``` **方法 1（線性搜索）** 線性搜索 x，計算 x 的出現次數并返回計數。 ## C++ ```cpp // C++ program to count occurrences of an element #include<bits/stdc++.h> using namespace std; // Returns number of times x occurs in arr[0..n-1] int countOccurrences(int arr[], int n, int x) { ????int res = 0; ????for (int i=0; i<n; i++) ????????if (x == arr[i]) ??????????res++; ????return res; } // Driver code int main() { ????int arr[] = {1, 2, 2, 2, 2, 3, 4, 7 ,8 ,8 }; ????int n = sizeof(arr)/sizeof(arr[0]); ????int x = 2; ????cout << countOccurrences(arr, n, x); ????return 0; } ```