题目:统计一个数字在排序数组中出现的次数。例如输入数组{1,2,3,3,3,3,4,5}和数字3,由于3在这个数组中出现了4次,因此输出4
// 找出目标数字(target)在有序数组中第一次出现的位置
int searchFirstPos(int A[], int N, int target)
{
if (N <= 0)
return -1;
int low = 0, high =N - 1;
while (low < high)
{
int mid = (low + high) / 2;
if (A[mid] < target)
{
low = mid + 1;
}
else
{
high = mid;
}
}
if (A[low] == target)
return low;
else
return -1;
}
// 找出目标数字(target)在有序数组中第后一次出现的位置
int searchLastPos(int A[], int N, int target)
{
if (N <= 0)
return -1;
int low = 0, high =N - 1;
while (low < high)
{
int mid = (low + high) / 2;
if (A[mid] > target)
{
high = mid - 1;
}
else
{
low = mid;
}
}
if (A[high] == target)
return high;
else
return -1;
}
int count(int A[], int N, int target)
{
int firstPos = searchFirstPos(A, N, target); // 第一次出现位置
if(firstPos == -1)
return 0;
int lastPos = searchLastPos(A, N, target); // 最后一次出现位置
return lastPos-firstPos+1; // 出现次数
}
更多参考:http://blog.youkuaiyun.com/luckyxiaoqiang/article/details/8937978</span>