LeetCode Course Schedule

题目

思路
明显的拓扑排序。
这里用的C写，用malloc动态分配内存给二维数组挺烦的，当做锻炼吧。

代码

bool canFinish(int numCourses, int** prerequisites, int prerequisitesRowSize, int prerequisitesColSize) {
    int * Indegrees;
    bool ** IsConnect;
    Indegrees = (int*)malloc(sizeof(int) * numCourses);
    IsConnect = (bool**)malloc(sizeof(bool*) * numCourses);
    for (int i = 0; i < numCourses; i++) {
        IsConnect[i] = (bool*)malloc(sizeof(bool) * numCourses);
    }
    //memset(Indegrees, 0, sizeof(Indegrees));
    //memset(IsConnect, false, sizeof(IsConnect));  something wrong here
    for (int i = 0; i < numCourses; i++) Indegrees[i] = 0;
    for (int i = 0; i < numCourses; i++) for (int j = 0; j < numCourses; j++) IsConnect[i][j] = false;
    for (int i = 0; i < prerequisitesRowSize; i++) {
        int To = prerequisites[i][0];
        for (int j = 1; j < prerequisitesColSize; j++) {
            if (0 <= prerequisites[i][j] && prerequisites[i][j] < numCourses && !IsConnect[prerequisites[i][j]][To]) {
                IsConnect[prerequisites[i][j]][To] = true;
                Indegrees[To]++;
            }
        }
    }
    int * Q = (int*)malloc(sizeof(int) * numCourses);
    int head = 0, tail = 0, Ans = 0;
    for (int i = 0; i < numCourses; i++) {
        if (Indegrees[i] == 0) {
            Q[tail++] = i;
            Ans++;
        }
    }
    while (head < tail) {
        for (int i = 0; i < numCourses; i++) {
            if (IsConnect[Q[head]][i]) {
                IsConnect[Q[head]][i] = false;
                Indegrees[i]--;
                if (Indegrees[i] == 0) {
                    Q[tail++] = i;
                    Ans++;
                }
            }
        }
        head++;
    }
    free(Indegrees);
    for (int i = 0; i < numCourses; i++) {
        free(IsConnect[i]);
    }
    free(Q);
    return Ans == numCourses;
}