代码实现：

/*** Return an array of arrays of size *returnSize.* The sizes of the arrays are returned as *returnColumnSizes array.* Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().*/// 交换
void swap(int *m, int *n) {int temp = *m;*m = *n;*n = temp;
}// 快排
void sort(int **nums, int l, int r) { // 左闭右开if (r - l <= 2) {if (r - l <= 1) { // 剩余个数：<= 1return;} else if (nums[r - 1][0] < nums[l][0]) { // 剩余个数：= 2 且后者小于前者 交换swap(&nums[r - 1][0], &nums[l][0]);swap(&nums[r - 1][1], &nums[l][1]);}}int x = nums[l][0];int y = nums[l][1];int i = l, j = r - 1;while (i < j) {while (i < j && nums[j][0] >= x) {j--;}if (i < j) {nums[i][0] = nums[j][0];nums[i][1] = nums[j][1];i++;}while (i < j && nums[i][0] <= x) {i++;}if (i < j) {nums[j][0] = nums[i][0];nums[j][1] = nums[i][1];j--;}}nums[i][0] = x, nums[i][1] = y;sort(nums, l, i);sort(nums, i + 1, r);
}int** merge(int **intervals, int intervalsSize, int *intervalsColSize, int *returnSize, int **returnColumnSizes){if (intervalsSize == 0) {return NULL;}*returnSize = 0;// 按左边界（从小到大）快排sort(intervals, 0, intervalsSize); // 左闭右开*returnColumnSizes = malloc(sizeof(int) * intervalsSize);int **res = malloc(sizeof(int*) * intervalsSize); // 记录结果int left = intervals[0][0];int right = intervals[0][1];for (int i = 1; i < intervalsSize; i++) {if (right >= intervals[i][0]) {right = right > intervals[i][1] ? right : intervals[i][1];} else {(*returnColumnSizes)[(*returnSize)] = 2;res[(*returnSize)] = malloc(sizeof(int) * 2);res[(*returnSize)][0] = left;res[(*returnSize)][1] = right;(*returnSize)++;left = intervals[i][0];right = intervals[i][1];}}// 记录合并的最后一个区间(*returnColumnSizes)[(*returnSize)] = 2;res[(*returnSize)] = malloc(sizeof(int) * 2);res[(*returnSize)][0] = left;res[(*returnSize)][1] = right;(*returnSize)++;return res;
}