面试题38 数字在排序数组中出现的次数

题目描述

统计一个数字在排序数组中出现的次数。

class Solution {
public:
    int getFirstK(vector<int> data ,int k){
        int low = 0, high = data.size() - 1, mid;
        while (low <= high){
            mid = (low + high) / 2;
            if ((mid > 0 && data[mid] == k && data[mid - 1] != k) || data[mid] == k && mid == 0)
                return mid;
            else if (data[mid] > k || data[mid - 1] == k)
                high = mid - 1;
            else
                low = mid + 1;
        }
        return -1;
    }
    
    int getLastK(vector<int> data ,int k){
        int low = 0, high = data.size() - 1, mid;
        while (low <= high){
            mid = (low + high) / 2;
            if ((mid < data.size() - 1 && data[mid] == k && data[mid + 1] != k) || data[mid] == k && mid == data.size() - 1)
                return mid;
            else if (data[mid] < k || data[mid + 1] == k)
                low = mid + 1;
            else
                high = mid - 1;
        }
        return -1;
    }
    
    int GetNumberOfK(vector<int> data ,int k) {
        int num = 0, length = data.size();
        if (length == 0)
            return num;
        int first = getFirstK(data ,k);
        int last = getLastK(data ,k); 
        
        if (first > -1 && last > -1)
            num = last - first + 1;
        return num;
    }
};