力扣双周赛 -- 117（容斥原理专场）
class Solution {
public:long long c2(long long n){return n > 1? n * (n - 1) / 2 : 0;}long long distributeCandies(int n, int limit) {return c2(n + 2) - 3 * c2(n - limit + 1) + 3 * c2(n - 2 * limit) - c2(n - 3 * limit - 1);}
};
class Solution {
public:long long c2(long long n){return n > 1? n * (n - 1) / 2 : 0;}long long distributeCandies(int n, int limit) {return c2(n + 2) - 3 * c2(n - limit + 1) + 3 * c2(n - 2 * limit) - c2(n - 3 * limit - 1);}
};