public static void Insert(SegNode root, long val)
{
root.Add++;
if (root.Lo == root.Hi)
{
return;
}
long mid = (root.Lo + root.Hi) >> 1;
if (val <= mid)
{
if (root.LeftChild == null)
{
root.LeftChild = new SegNode(root.Lo, mid);
}
Insert(root.LeftChild, val);
}
else
{
if (root.RightChild == null)
{
root.RightChild = new SegNode(mid + 1, root.Hi);
}
Insert(root.RightChild, val);
}
}
/// <summary>
/// 归并排序
/// </summary>
/// <param name="nums"></param>
/// <param name="lower"></param>
/// <param name="upper"></param>
/// <returns></returns>
//public static int CountRangeSum(int[] nums, int lower, int upper)
//{
// long s = 0;
// long[] sum = new long[nums.Length + 1];
// for (int i = 0; i < nums.Length; ++i)
// {
// s += nums[i];
// sum[i + 1] = s;
// }
// return CountRangeSumRecursive(sum, lower, upper, 0, sum.Length - 1);
//}
/// <summary>
/// 归并排序递归
/// </summary>
/// <param name="sum"></param>
/// <param name="lower"></param>
/// <param name="upper"></param>
/// <param name="left"></param>
/// <param name="right"></param>
/// <returns></returns>
//public static int CountRangeSumRecursive(long[] sum, int lower, int upper, int left, int right)
//{
// if (left == right)
// {
// return 0;
// }
// else
// {
// int mid = (left + right) / 2;
// int n1 = CountRangeSumRecursive(sum, lower, upper, left, mid);
// int n2 = CountRangeSumRecursive(sum, lower, upper, mid + 1, right);
// int ret = n1 + n2;
// // 首先统计下标对的数量
// int i = left;
// int l = mid + 1;
// int r = mid + 1;
// while (i <= mid)
// {
// while (l <= right && sum[l] - sum[i] < lower)
// {
// l++;
// }
// while (r <= right && sum[r] - sum[i] <= upper)
// {
// r++;
// }
// ret += r - l;
// i++;
// }
// // 随后合并两个排序数组
// int[] sorted = new int[right - left + 1];
// int p1 = left, p2 = mid + 1;
// int p = 0;
// while (p1 <= mid || p2 <= right)
// {
// if (p1 > mid)
// {
// sorted[p++] = (int)sum[p2++];
// }
// else if (p2 > right)
// {
// sorted[p++] = (int)sum[p1++];
// }
// else
// {
// if (sum[p1] < sum[p2])
// {
// sorted[p++] = (int)sum[p1++];
// }
// else
// {
// sorted[p++] = (int)sum[p2++];
// }
// }
// }
// for (int j = 0; j < sorted.Length; j++)
// {
// sum[left + j] = sorted[j];
// }
// return ret;
// }
//}
/// <summary>
/// 线段树
/// </summary>
public static int CountRangeSum(int[] nums, int lower, int upper)
{
long sum = 0;
long[] preSum = new long[nums.Length + 1];
for (int i = 0; i < nums.Length; i++)
{
sum += nums[i];
preSum[i + 1] = sum;
}
long lbound = long.MaxValue, rbound = long.MinValue;
foreach (var x in preSum)
{
lbound = Math.Min(Math.Min(lbound, x), Math.Min(x - lower, x - upper));
rbound = Math.Max(Math.Max(rbound, x), Math.Max(x - lower, x - upper));
}
SegNode root = new SegNode(lbound, rbound);
int res = 0;
foreach (var x in preSum)
{
res += Count(root, x - upper, x - lower);
Insert(root, x);
}
return(res);
}
public SegNode(long left, long right)
{
Lo = left;
Hi = right;
Add = 0;
LeftChild = null;
RightChild = null;
}
public static int Count(SegNode root, long left, long right)
{
if (root == null)
{
return(0);
}
if (left > root.Hi || right < root.Lo)
{
return(0);
}
if (left <= root.Lo && root.Hi <= right)
{
return(root.Add);
}
return(Count(root.LeftChild, left, right) + Count(root.RightChild, left, right));
}