## 三、解题代码

``````public class Test {
/**
* 找排序数组中k第一次出现的位置
*
* @param data
* @param k
* @param start
* @param end
* @return
*/
private static int getFirstK(int[] data, int k, int start, int end) {
if (data == null || data.length < 1 || start > end) {
return -1;
}

int midIdx = start + (end - start) / 2;
int midData = data[midIdx];

if (midData == k) {
if (midIdx > 0 && data[midIdx - 1] != k || midIdx == 0) {
return midIdx;
} else {
end = midIdx - 1;
}
} else if (midData > k) {
end = midIdx - 1;
} else {
start = midIdx + 1;
}

return getFirstK(data, k, start, end);
}

/**
* 找排序数组中k最后一次出现的位置
*
* @param data
* @param k
* @param start
* @param end
* @return
*/
private static int getLastK(int[] data, int k, int start, int end) {
if (data == null || data.length < 1 || start > end) {
return -1;
}

int midIdx = start + (end - start) / 2;
int midData = data[midIdx];

if (midData == k) {
if (midIdx + 1 < data.length && data[midIdx + 1] != k || midIdx == data.length - 1) {
return midIdx;
} else {
start = midIdx + 1;
}
} else if (midData < k) {
start = midIdx + 1;
} else {
end = midIdx - 1;
}

return getLastK(data, k, start, end);
}

/**
* 题目：统计一个数字：在排序数组中出现的次数
* @param data
* @param k
* @return
*/
public static int getNumberOfK(int[] data, int k) {
int number = 0;
if (data != null && data.length > 0) {
int first = getFirstK(data, k, 0, data.length - 1);
int last = getLastK(data, k, 0, data.length - 1);

if (first > -1 && last > -1) {
number = last - first + 1;
}
}

return number;
}
}``````