【C语言刷力扣】2006.差的绝对值为K的数对数目

题目;

法一 解题思路：

        |num[i] - num[j]| = k 可以理解为 num[j] = num[i] + k 和 num[j] = num[i] - k 两种情况。

int countKDifference(int* nums, int numsSize, int k) {
    int ans = 0;
    int hash[101];
    memset(hash, 0, sizeof(hash));
    for (int i = 0; i < numsSize; i++) {
        int x = nums[i] + k;
        if (x >= 1 && x <= 100) ans += hash[x];
        x = nums[i] - k;
        if (x >= 1 && x <= 100) ans += hash[x];

        hash[ nums[i] ]++;
    }
    return ans;
}

法二 动态分配

typedef struct  {
    int key;            
    int val;
    UT_hash_handle hh;
} HashEntry;

int countKDifference(int* nums, int numsSize, int k){
    int ans = 0;
    HashEntry * cnt = NULL;
    for (int j = 0; j < numsSize; ++j) {
        HashEntry * pEntry = NULL;
        int curr = nums[j] - k;
        HASH_FIND(hh, cnt, &curr, sizeof(int),pEntry);
        if (NULL != pEntry) {
            ans += pEntry->val;
        }
        curr = nums[j] + k;
        HASH_FIND(hh, cnt, &curr, sizeof(int), pEntry);
        if (NULL != pEntry) {
            ans += pEntry->val;
        }
        HASH_FIND(hh, cnt, &nums[j], sizeof(int), pEntry);
        if (NULL == pEntry) {
            pEntry = (HashEntry *)malloc(sizeof(HashEntry));
            pEntry->key = nums[j];
            pEntry->val = 1;
            HASH_ADD(hh, cnt, key, sizeof(int), pEntry);
        } else {
            ++pEntry->val;
        }
    }
    HashEntry * curr = NULL, * next = NULL;
    HASH_ITER(hh, cnt, curr, next) {
        HASH_DEL(cnt, curr);
    }
    return ans;
}