代码实现：

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
char** summaryRanges(int* nums, int numsSize, int *returnSize) {
    char **res = malloc(sizeof(char*) * numsSize);
    *returnSize = 0;
    int i, j;
    for (i = 0; i < numsSize; i++) { // i: 区间左边第一个
        for (j = i + 1; j < numsSize; j++) { // j-1：区间右边第一个
            if (nums[j] != nums[j - 1] + 1) {
                break;
            }
        }
        // [i...j-1]
        char *ret = malloc(sizeof(char) * (25));
        sprintf(ret, "%d", nums[i]);
        if (i != j - 1) {
            sprintf(ret + strlen(ret), "->");
            sprintf(ret + strlen(ret), "%d", nums[j - 1]);
        }
        ret[strlen(ret)] = '\0';
        res[(*returnSize)++] = ret;
        i = j - 1;
    }
    return res;
}