Given a target number and an integer array sorted in ascending order. Find the total number of occurrences of target in the array.

Have you met this question in a real interview?

Yes

Example

Given[1, 3, 3, 4, 5]and target =3, return2.

Given[2, 2, 3, 4, 6]and target =4, return1.

Given[1, 2, 3, 4, 5]and target =6, return0.

Challenge

Time complexity in O(logn)

class Solution {
public:
    /**
     * @param A an integer array sorted in ascending order
     * @param target an integer
     * @return an integer
     */
    int totalOccurrence(vector<int>& A, int target) {
        // Write your code here
        if (A.empty())
            return 0;

        // find first element
        int start = 0, end = A.size() - 1;
        while (start + 1 < end) {
            int mid = start + (end - start >> 1);
            if (A[mid] < target)
                start = mid;
            else
                end = mid;
        }

        int first, last;
        if (A[start] == target)
            first = start;
        else if (A[end] == target)
            first = end;
        else 
            first = -1;

        // find last element 
        start = 0, end = A.size() - 1;
        while (start + 1 < end) {
            int mid = start + (end - start >> 1);
            if (A[mid] > target)
                end = mid;
            else
                start = mid;
        }

        if (A[end] == target)
            last = end;
        else if (A[start] == target)
            last = start;
        else 
            last = -1;

        if (first != -1)
            return last - first + 1;

        return 0;
    }
};