ri tnnd....
> 这道题只要依次按每个桥把坐标对折一下就可以了....
> 
> 
> 
> 		res = -1;
> 		memset(delta, -1, sizeof(delta));
> 		delta[X[0]] = 0;
> 		for(i = 1; i < n; ++i) {
> 			int p = X[i] - (int)(sqrt((double)Y[i] * Y[i] - (double)(Y[i] - Y[0]) * (Y[i] - Y[0])) + 1e-12);
> 			if(p < 0) p = 0;
> 			for(j = p; j < X[i]; ++j) {
> 				if(delta[j] == -1) continue;
> 				j1 = 2 * X[i] - j;
> 				if(j1 < X[n - 1]) {
> 					if(delta[j1] == -1 || delta[j] + 1 < delta[j1])
> 						delta[j1] = delta[j] +  1;
> 				} else {
> 					if(res == -1 || delta[j] + 1 < res)
> 						res = delta[j] + 1;
> 				}
> 			}
> 		}