統計一個數字在排序陣列中出現的次數。

思路：排序陣列一定要想到二分法查詢

package co.com.jianzhioffer;

import java.io.ObjectInputStream.GetField;

public class Solution38 {
	public static int GetNumberOfK(int[] array, int k) {
		int length = array.length;
		if (array == null || 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;
	}

	// 迴圈寫法
	 private static int getFirstK(int[] array, int k, int low, int high) {
	 int length = array.length;
	 int mid = (low + high) >> 1;
	 while (low <= high) {
	 if (array[mid] > k) {
	 high = mid - 1;
	 } else if (array[mid] < k) {
	
	 low = mid + 1;
	 } else if (mid - 1 >= 0 && array[mid - 1] == k) {
	 high = mid - 1;
	 } else {
	 return mid;
	 }
	 mid = (low + high) >> 1;
	
	 }
	 return -1;
	
	 }

	// 遞迴寫法
	private static int getFirstK(int[] array, int k, int start, int end) {
		if (start > end) {
			return -1;
		}
		int mid = (start + end) >> 1;
		if (array[mid] > k) {
			return getFirstK(array, k, start, mid - 1);
		} else if (array[mid] < k) {
			return getFirstK(array, k, mid + 1, end);
		} else if (mid - 1 >= 0 && array[mid - 1] == k) {
			return getFirstK(array, k, start, mid - 1);
		} else {
			return mid;

		}

	}

	private static int getLastK(int[] array, int k, int low, int high) {
		int length = array.length;
		int mid = (low + high) >> 1;
		while (low <= high) {
			if (array[mid] > k) {
				high = mid - 1;
			} else if (array[mid] < k) {

				low = mid + 1;
			} else if (mid + 1 < length && array[mid + 1] == k) {
				low = mid + 1;
			} else {
				return mid;
			}

			mid = (low + high) >> 1;

		}
		return -1;

	}

	public static void main(String[] args) {
		int[] array = { 3, 3, 3, 3, 4, 5 };
		System.out.println(GetNumberOfK(array, 3));
	}
}