974. 和可被 K 整除的子数组

974. 和可被 K 整除的子数组

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C代码：哈希表+前缀和

typedef struct{
    int val;
    int cnt;
    UT_hash_handle hh;
} HashTable;

int subarraysDivByK(int* nums, int numsSize, int k){
    HashTable* head = NULL;
    HashTable* out = NULL;
    int sum = 0;
    int cnt = 0;

    out = (HashTable*)malloc(sizeof(HashTable));  // 0
    out->val = 0;
    out->cnt = 1;
    HASH_ADD_INT(head, val, out);

    for (int i = 0; i < numsSize; ++i) {
        sum += nums[i];
        int val = (sum % k + k) % k;  // (sum2-sum1)%k == 0; sum2 % k == sum1%k; 适合整数、但是负数不行 当被除数为负数时取模结果为负数，需要纠正
        HASH_FIND_INT(head, &val, out);
        if (out == NULL) {
            out = (HashTable*)malloc(sizeof(HashTable));
            out->val = val;
            out->cnt = 1;
            HASH_ADD_INT(head, val, out);
        } else {
            cnt += out->cnt;
            out->cnt++;  // 叠加次数
        }
    }

    return cnt;
}
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