其它pta数据结构编程题请参见：pta
主要用到了深度优先搜索。
1 #include <iostream> 2 using namespace std; 3 4 struct Vertex 5 { 6 int x; 7 int y; 8 bool marked; 9 }G[100]; 10 11 int N; //总鳄鱼数 12 int D; //可以跳的距离 13 bool dfs(Vertex& v); 14 bool firstJump(Vertex v); 15 bool jump(Vertex v1, Vertex v2); 16 bool success(Vertex v); //可以跳到岸上 17 18 int main() 19 { 20 int i; 21 cin >> N >> D; 22 for (i = 0; i < N; i++) 23 cin >> G[i].x >> G[i].y; 24 25 bool canEscape = false; 26 for (i = 0; i < N; i++) 27 { 28 if (!G[i].marked && firstJump(G[i])) 29 canEscape = dfs(G[i]); 30 if (canEscape) break; 31 } 32 if (canEscape) cout << "Yes"; 33 else cout << "No"; 34 return 0; 35 } 36 37 bool firstJump(Vertex v) 38 { 39 return v.x * v.x + v.y * v.y <= (15 + D) * (15 + D); 40 } 41 42 bool dfs(Vertex& v) 43 { 44 bool canEscape = false; 45 v.marked = true; 46 if (success(v)) return true; 47 for (int i = 0; i < N; i++) 48 { 49 if (!G[i].marked && jump(v, G[i])) 50 canEscape = dfs(G[i]); 51 if (canEscape) break; 52 } 53 return canEscape; 54 } 55 56 bool success(Vertex v) 57 { 58 if (v.x <= D - 50 || v.x >= 50 - D || v.y <= D - 50 || v.y >= 50 - D) 59 return true; 60 return false; 61 } 62 63 bool jump(Vertex v1, Vertex v2) 64 { 65 return (v1.x - v2.x) * (v1.x - v2.x) + (v1.y - v2.y) * (v1.y - v2.y) <= D*D; 66 }