【leetcode】210. 课程表 II

int* findOrder(int numCourses, int** prerequisites, int prerequisitesSize, int* prerequisitesColSize, int* returnSize){
    int** edges = (int**)calloc(numCourses, sizeof(int*));
    int* edgesColSize = (int*)calloc(numCourses, sizeof(int));
    int* cnt = (int*)calloc(numCourses, sizeof(int));
    int* arr = (int*)calloc(numCourses, sizeof(int));

    *returnSize = 0;
    int i, a, b, left=0;

    for (i = 0; i < numCourses; i++)
        edges[i] = (int*)malloc(0);

    for (i = 0; i < prerequisitesSize; i++){
        a = prerequisites[i][1]; b = prerequisites[i][0];
        edges[a] = (int*)realloc(edges[a], sizeof(int)* ++edgesColSize[a]);
        edges[a][edgesColSize[a] - 1] = b;
        cnt[b]++;
    }
    for (i = 0; i < numCourses; i++){
        if (cnt[i] == 0)
            arr[(*returnSize)++] = i;
    }
    while (left < *returnSize){
        int u = arr[left++];
        for (i = 0; i < edgesColSize[u]; i++){
            cnt[edges[u][i]]--;
            if (cnt[edges[u][i]]==0)
                arr[(*returnSize)++] = edges[u][i];
        }
    }
    if (*returnSize != numCourses)
        *returnSize = 0;
    return arr;
}