区间列表的交集(Interval List Intersections)

给定两个由一些 闭区间 组成的列表，firstList 和 secondList ，其中 firstList[i] = [start_i, end_i] 而 secondList[j] = [start_j, end_j] 。每个区间列表都是成对 不相交 的，并且 已经排序 。

返回这 两个区间列表的交集 。

形式上，闭区间 [a, b]（其中 a <= b）表示实数 x 的集合，而 a <= x <= b 。

两个闭区间的交集是一组实数，要么为空集，要么为闭区间。例如，[1, 3] 和 [2, 4] 的交集为 [2, 3] 。

示例 1： 图裂了

输入：firstList = [[0,2],[5,10],[13,23],[24,25]], secondList = [[1,5],[8,12],[15,24],[25,26]]
输出：[[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]

示例 2：

输入：firstList = [[1,3],[5,9]], secondList = []
输出：[]

示例 3：

输入：firstList = [], secondList = [[4,8],[10,12]]
输出：[]

示例 4：

输入：firstList = [[1,7]], secondList = [[3,10]]
输出：[[3,7]]

提示：

0 <= firstList.length, secondList.length <= 1000
firstList.length + secondList.length >= 1
0 <= start_i < end_i <= 10^9
end_i < start_{i+1}
0 <= start_j < end_j <= 10^9
end_j < start_{j+1}

/**
 * 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().
 */
/**
 * 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().
 */
int** intervalIntersection(
        int** A,
        int ASize,
        int* AColSize,
        int** B,
        int BSize,
        int* BColSize,
        int* returnSize,
        int** returnColumnSizes){
    int** ans = NULL;
    int ansSize = 0;

    int i = 0, j = 0;
    while (i<ASize && j<BSize){
        if (A[i][0] <= B[j][0] && B[j][1] <= A[i][1]) {
            int *C = malloc(sizeof(int)*2);
            C[0] = B[j][0];
            C[1] = B[j][1];

            ansSize++;
            ans = realloc(ans, ansSize*sizeof(int*));
            ans[ansSize-1] = C;
        } else if (B[j][0] <= A[i][0] && A[i][1] <= B[j][1]) {
            int *C = malloc(sizeof(int)*2);
            C[0] = A[i][0];
            C[1] = A[i][1];

            ansSize++;
            ans = realloc(ans, ansSize*sizeof(int*));
            ans[ansSize-1] = C;
        } else if (A[i][0] <= B[j][0] && A[i][1]<=B[j][1] && A[i][1] >= B[j][0]){
            int *C = malloc(sizeof(int)*2);
            C[0] = B[j][0];
            C[1] = A[i][1];

            ansSize++;
            ans = realloc(ans, ansSize*sizeof(int*));
            ans[ansSize-1] = C;
        } else if (B[j][0] <= A[i][0] && B[j][1] <= A[i][1] && B[j][1] >= A[i][0]) {
            int *C = malloc(sizeof(int)*2);
            C[0] = A[i][0];
            C[1] = B[j][1];

            ansSize++;
            ans = realloc(ans, ansSize*sizeof(int*));
            ans[ansSize-1] = C;
        }
        if (A[i][1]<=B[j][1]){
            i++;
        }else{
            j++;
        }
    }

    *returnSize= ansSize;
    int* ansColSize = malloc(ansSize*sizeof(int));
    for (int k = 0; k < ansSize; ++k) {
        ansColSize[k] = 2;
    }
    *returnColumnSizes = ansColSize;
    return ans;
}

最暴力的手段，直接列举所有的可能性