lc

lc2964

枚举中间+hash

class Solution {

public:

int divisibleTripletCount(vector<int>& nums, int d)

{

int n = nums.size();

if (n < 3) return 0;

int ret = 0;

unordered_map<int, int> hash;

hash[nums[0] % d]++;

// 枚举中间

for (int i = 1; i < n - 1; ++i) {

int mod_i = nums[i] % d;

// 枚举后面

for (int j = i + 1; j < n; ++j) {

int mod_j = nums[j] % d;

int t = (d - (mod_i + mod_j) % d) % d;

ret += hash[t];

}

hash[mod_i]++;

}

return ret;

}

};