非常简单...

#include<iostream>
using namespace std;

int main() {
    int a, b, c;
    cin >> a >> b >> c;
    if(a > b) swap(a, b);
    if(a > c) swap(a, c);
    if(b > c) swap(b, c);
    if(a + b <= c) {
        cout << "Not triangle" << endl; 
        return 0;//撤离失败
    }
    if(a * a + b * b == c * c) 
        cout << "Right triangle" << endl;
    if(a * a + b * b > c * c)
        cout << "Acute triangle" << endl;
    if(a * a + b * b < c * c)
        cout << "Obtuse triangle" << endl;
    if((a == b || a == c)||(c == b || a == c)||(a == b || b == c))
        cout << "Isosceles triangle" << endl;
    if(a == b && a == c && b == c)
        cout << "Equilateral triangle" << endl;
    return 0;
}