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
//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;
}
}
来源：https://www.cnblogs.com/MarkLeeBYR/p/9774275.html