题目链接
题目思路 【Codeforces Round #643 (Div. 2) C. Count Triangles 题解（思维）】显然是找x+y>z即可，其实只要枚举x+y即可，自己好菜qwq
代码
#include
#include
using namespace std;
typedef long long ll;
int a,b,c,d;
ll ans;
int main(){
scanf("%d %d %d %d",&a,&b,&c,&d);
for(int i=max(a+b,c);
i<=b+c;
i++){//枚举x+y
int l=max(a,i-c),r=min(b,i-b);
//枚举x的长度
ans+=1ll*(r-l+1)*(min(i-1,d)-c+1);
}
printf("%lld\n",ans);
return 0;
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