题目：
题解：
class Solution {public 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);}public 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long[] sorted = new long[right - left + 1];int p1 = left, p2 = mid + 1;int p = 0;while (p1 <= mid || p2 <= right) {if (p1 > mid) {sorted[p++] = sum[p2++];} else if (p2 > right) {sorted[p++] = sum[p1++];} else {if (sum[p1] < sum[p2]) {sorted[p++] = sum[p1++];} else {sorted[p++] = sum[p2++];}}}for (int j = 0; j < sorted.length; j++) {sum[left + j] = sorted[j];}return ret;}}
}