c++中如何统计有序数组中元素出现次数_c++有序数组元素出现次数统计

#include <vector>
#include <algorithm>
#include <iostream>
<p>int countOccurrences(const std::vector<int>& arr, int target) {
auto left = std::lower_bound(arr.begin(), arr.end(), target);
auto right = std::upper_bound(arr.begin(), arr.end(), target);
return right - left;
}</p><p>int main() {
std::vector<int> arr = {1, 2, 2, 2, 3, 4, 5};
int target = 2;
std::cout << target << " 出现了 " << countOccurrences(arr, target) << " 次\n";
return 0;
}</p>

int findLeftBound(const std::vector<int>& arr, int target) {
    int left = 0, right = arr.size();
    while (left < right) {
        int mid = left + (right - left) / 2;
        if (arr[mid] < target) {
            left = mid + 1;
        } else {
            right = mid;
        }
    }
    return left;
}

int findRightBound(const std::vector<int>& arr, int target) {
    int left = 0, right = arr.size();
    while (left < right) {
        int mid = left + (right - left) / 2;
        if (arr[mid] <= target) {
            left = mid + 1;
        } else {
            right = mid;
        }
    }
    return left;
}

int count = findRightBound(arr, target) - findLeftBound(arr, target);