题目:
题解:
cpp
class Solution {
public:
int numberOfArithmeticSlices(vector<int> &nums) {
int ans = 0;
int n = nums.size();
vector<unordered_map<long long, int>> f(n);
for (int i = 0; i < n; ++i) {
for (int j = 0; j < i; ++j) {
long long d = 1LL * nums[i] - nums[j];
auto it = f[j].find(d);
int cnt = it == f[j].end() ? 0 : it->second;
ans += cnt;
f[i][d] += cnt + 1;
}
}
return ans;
}
};