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Обсуждение задачи 1600. АэропортFaeton (Kyiv - Mohyla Academy) could anyone give some tests? [12] // Задача 1600. Аэропорт 2 мар 2008 22:20 I always have WA. The idea is simple: get derivative from distance. assume a1=x[i]-x[j],a2=y[i]-y[j],a3=z[i]-z[j], b1 = vx[i]-vx[j],b2 = vy[i]-vy[j],b3 = vz[i]-vz[j]. Then we should solve quadric equation ax^2+bx+c to find time, where a=a = (b1*b1+b2*b2+b3*b3), b = 2*(a1*b1+a2*b2+a3*b3), c = (a1*a1+a2*a2+a3*a3)-d; where i'm wrong? Edited by author 02.03.2008 22:32 KIRILL(ArcSTUpid coder:) Re: could anyone give some tests? [9] // Задача 1600. Аэропорт 3 мар 2008 04:34 it's right if d = d * d check negative roots be careful with float point try this random test 4 15.0 15.0 1.4 -3.0 3.0 54.0 130.0 65.0 23.0 4.0 5.0 3.0 34.4 23.0 57.0 5.0 8.0 4.0 31.4 7.0 34.0 7.0 123.0 76.0 54.4 ALARM! 0.124 3 4 Edited by author 03.03.2008 04:35 Edited by author 03.03.2008 04:36 Anastas Re: could anyone give some tests? [1] // Задача 1600. Аэропорт 3 мар 2008 20:16 Please give me tests when the roots are negative!! KIRILL(ArcSTUpid coder:) Re: could anyone give some tests? // Задача 1600. Аэропорт 3 мар 2008 22:32 it's not hard 2 0.1 0 1 0 1 1 0 0 0 0 1 -1 0 OK roots -0.45 and -0.55 one more test(with positive roots) 2 0.1 -10000 -10000 0 0.1 0.1 0 -10000 10000 0 0.1 0 0 ALARM! 199999.000 1 2 SuperLight Re: could anyone give some tests? [3] // Задача 1600. Аэропорт 4 мар 2008 14:46 Why we should check negative roots if d = d*d ??? what happen when d==d*d?? Edited by author 04.03.2008 17:24 KIRILL(ArcSTUpid coder:) Re: could anyone give some tests? [2] // Задача 1600. Аэропорт 4 мар 2008 19:46 SuperLight писал(a) 4 марта 2008 14:46 Why we should check negative roots if d = d*d ??? Edited by author 04.03.2008 17:24 it's right if d = d * d , :) check negative roots what happen when d==d*d?? nothing! I just wanted to say that we should replace d with d*d before calculations Edited by author 04.03.2008 19:51 SuperLight Re: could anyone give some tests? [1] // Задача 1600. Аэропорт 4 мар 2008 22:33 If I`m not mistaken, x in equation ax^2+bx+c is time from the begging...so we shouldn`t check negative roots, because it was before the start point! What`s wrong? I can`t understand... KIRILL(ArcSTUpid coder:) Re: could anyone give some tests? // Задача 1600. Аэропорт 5 мар 2008 02:30 SuperLight писал(a) 4 марта 2008 22:33 If I`m not mistaken, x in equation ax^2+bx+c is time from the begging...so we shouldn`t check negative roots, because it was before the start point! What`s wrong? I can`t understand... in this case check == ignore we chose smallest positive root you can send me your code I'll check it in this case check != ignore :) Beksinski Re: could anyone give some tests? [2] // Задача 1600. Аэропорт 6 мар 2008 13:50 Please, give me some hints related to "be careful with float point"? KIRILL(ArcSTUpid coder:) Re: could anyone give some tests? [1] // Задача 1600. Аэропорт 6 мар 2008 20:40 use eps for example if (discriminant<0) continue; // it's wrong if (discriminant+1e-9<0) continue; // it's right Edited by author 06.03.2008 20:41 Beksinski Re: could anyone give some tests? // Задача 1600. Аэропорт 10 мар 2008 00:25 Thank you! I used #define EPS 0.000000001 if(discr>=-EPS) and had got AC! SuperLight Re: could anyone give some tests? // Задача 1600. Аэропорт 3 мар 2008 23:24 Edited by author 03.03.2008 23:43 Edited by author 03.03.2008 23:43 unlucky [Vologda SPU] Re: could anyone give some tests? // Задача 1600. Аэропорт 8 ноя 2009 00:10 Faeton (Kyiv - Mohyla Academy) писал(a) 2 марта 2008 22:20 I always have WA. Don't use this formula. It's not right.The idea is simple: get derivative from distance. assume a1=x[i]-x[j],a2=y[i]-y[j],a3=z[i]-z[j], b1 = vx[i]-vx[j],b2 = vy[i]-vy[j],b3 = vz[i]-vz[j]. Then we should solve quadric equation ax^2+bx+c to find time, where a=a = (b1*b1+b2*b2+b3*b3), b = 2*(a1*b1+a2*b2+a3*b3), c = (a1*a1+a2*a2+a3*a3)-d; where i'm wrong? Edited by author 02.03.2008 22:32 Silly author mistake =) |