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| class Solution {
int count = 0;
public int reversePairs(int[] nums) {
mergeSort(nums, 0, nums.length - 1);
return count;
}
private void mergeSort(int[] nums, int left, int right) {
if (left >= right) return ;
int mid = left + (right - left) / 2;
mergeSort(nums, left, mid);
mergeSort(nums, mid + 1, right);
merge(nums, left, mid, right);
}
private void merge(int[] nums, int left, int mid, int right) {
int i = left;
while (i <= mid) {
int j = mid + 1;
while (i <= mid) {
while (j <= right && (long) nums[i] > 2 * (long) nums[j]) {
j++;
}
count += j - mid - 1;
i++;
}
}
i = left;
int j = mid + 1, k = 0;
int[] arr = new int[right - left + 1];
while(i <= mid || j <= right) {
if (i > mid) {
arr[k++] = nums[j++];
} else if (j > right) {
arr[k++] = nums[i++];
} else {
if (nums[i] <= nums[j]) {
arr[k++] = nums[i++];
} else {
arr[k++] = nums[j++];
}
}
}
k = 0;
while (k < arr.length) {
nums[left++] = arr[k++];
}
}
}
|