Ultraviolet A 718-Skyscraper Floors (number theory)

Ultraviolet A 718-Skyscraper Floors

Question Link

There is an e-elevator in an f-storey upstairs. Each elevator has x, and y indicates that y + k * x can be reached, now I want to ask if I can reach B from layer a (there is no restriction on how to change to the elevator in the middle)

Train of Thought: For the transfer between two elevator rooms, As long as y [I] + xx x [I] = y [j] + yy y [j]. next, you can use Extended Euclidean solutions to find the general solutions of x and y, and then use the general solution range x'> = 0, y'> = 0, x [I] x' + y [I] <= f, x [j] y' + y [j] <= f, and the upper and lower limits of t in the general solution are obtained, then we can determine that there is no solution, and then we will build a map, and change the two sides of the elevator to build the edge, and then let a, B and the elevator determine whether they can be reached, to build the edge, the last dfs can be used to determine whether it can be reached.

Code:

#include 
 
  #include 
  
   #include 
   
    #include 
    
     using namespace std;const int INF = 0x3f3f3f3f;int t, f, e, a, b, x[105], y[105], vis[105];vector
     
       g[105];int exgcd(int a, int b, int &x, int &y) {if (!b) {x = 1; y = 0; return a;}int d = exgcd(b, a % b, y, x);y -= a / b * x;return d;}void build(int v, int u, int i) {if (v < y[i]) return;if ((v - y[i]) % x[i] == 0) {g[u].push_back(i);g[i].push_back(u); }}void build2(int i, int j) {int xx, yy;int a = x[i], b = -x[j], c = y[j] - y[i];int d = exgcd(a, b, xx ,yy);if (c % d) return;int down = -INF;int up = INF;if (b / d > 0) { down = max(down, (int)ceil(-xx * c * 1.0 / b)); up = min(up, (int)floor(((f - y[i]) * 1.0 * d / x[i] - xx * c * 1.0) / b));}else {down = max(down, (int)ceil(((f - y[i]) * 1.0 * d / x[i] - xx * c * 1.0) / b)); up = min(up, (int)floor(-xx * c * 1.0 / b));}if (a / d > 0) {down = max(down, (int)ceil((yy * c * 1.0 - (f - y[j]) * 1.0 * d / x[j]) / a)); up = min(up, (int)floor(yy * c * 1.0 / a));}else { down = max(down, (int)ceil(yy * c * 1.0 / a)); up = min(up, (int)floor((yy * c * 1.0 - (f - y[j]) * 1.0 * d / x[j]) / a));}if (down > up) return;g[i].push_back(j);g[j].push_back(i);}bool dfs(int u) {if (u == e + 1) return true;vis[u] = 1;for (int i = 0; i < g[u].size(); i++) {int v = g[u][i];if (vis[v]) continue;if (dfs(v)) return true; } return false;}int main() {scanf("%d", &t);while (t--) {memset(g, 0, sizeof(g));scanf("%d%d%d%d", &f, &e, &a, &b);for (int i = 1; i <= e; i++) {scanf("%d%d", &x[i], &y[i]);   build(a, 0, i);   build(b, e + 1, i);}for (int i = 1; i <= e; i++) {for (int j = i + 1; j <= e; j++) {build2(i, j);   }  }  memset(vis, 0, sizeof(vis));  if (dfs(0)) printf("It is possible to move the furniture.\n");  else printf("The furniture cannot be moved.\n"); }return 0;}