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。

因为在一个排序数组中，所以优先想到二分查找，分别找出第一个和最后一个

public class Solution {

    public int GetNumberOfK(int [] array , int k) {

        int length = array.length;

        if (length == 0)

            return 0;

        int firstk = getFirstK(array, k, 0, length - 1);

        int lastk = getLastK(array, k, 0, length - 1);

        if (firstk != -1 && lastk != -1)

            return lastk - firstk + 1;

        return 0;

    }

 

    private int getFirstK(int[] array , int k, int start, int end) {

        while (start <= end) {

            int mid = start + (end - start) / 2;

            if (array[mid] > k)

                end = mid - 1;

            else if (array[mid] < k)

                start = mid + 1;

            else if (mid - 1 >= 0 && array[mid - 1] == k)

                end = mid - 1;

            else 

                return mid;                    

        }

        return -1;

    }
//循环

    private int getLastK(int[] array , int k, int start, int end) {    

        while (start <= end) {

            int mid = start + (end - start) / 2;

            if (array[mid] > k)

                end = mid - 1;

            else if (array[mid] < k)

                start = mid + 1;

            else if (mid + 1 < array.length && array[mid + 1] == k)

                start = mid + 1;

            else 

                return mid;                    

        }

        return -1;

    }

}