pta编程题19 Saving James Bond 2

Posted 2020-11-02 bloglxc

其它pta数据结构编程题请参见：pta

题目

和简单版本不同的是，简单版本只需判断能否到达岸边，而这个版本要求求出最少跳数的路径。

简单版本用dfs实现，而这道题用BFS实现。

注意：

岛半径为7.5，而不是15。另外注意一步跳到岸边的情况。

  1 #include <iostream>
  2 #include <vector>
  3 #include <math.h>
  4 using namespace std;
  5 const int maxInt = 65535;
  6 
  7 int N, D;
  8 struct point
  9 {
 10     int x, y;
 11 }G[100];
 12 
 13 struct queue
 14 {
 15     int arr[100];
 16     int head = 0;
 17     int tail = 0;
 18 };
 19 
 20 void enQueue(int i, queue& q);
 21 int deQueue(queue& q);
 22 bool isEmpty(queue q);
 23 
 24 bool firstJump(int i);
 25 bool jump(int i, int j);
 26 bool toBank(int i);
 27 bool bfs(int s, vector<int>& p);
 28 bool shorter(vector<int> path1, vector<int> path2);
 29 
 30 int main()
 31 {
 32     int i;
 33     cin >> N >> D;
 34     for (i = 0; i < N; i++)
 35         cin >> G[i].x >> G[i].y;
 36 
 37     bool first = true;
 38     vector<int> path, minPath;
 39     for (i = 0; i < N; i++)
 40     {
 41         if (firstJump(i) && bfs(i, path))
 42         {
 43             if (first) //第一个可达到岸边的鳄鱼
 44             {
 45                 minPath = path;
 46                 first = false;
 47             }
 48             else if (shorter(path, minPath))
 49                 minPath = path;
 50         }
 51     }
 52 
 53     if (first) cout << 0; //岸边不可达
 54     else if (7.5 + D >= 50) //直接跳到岸边
 55         cout << 1;
 56     else {
 57         cout << minPath.size() + 1 << endl;
 58         for (i = minPath.size() - 1; i >= 0; i--)
 59         {
 60             int id = minPath[i];
 61             cout << G[id].x << " " << G[id].y << endl;
 62         }
 63     }
 64     return 0;
 65 }
 66 
 67 bool firstJump(int i)
 68 {
 69     bool a = pow(G[i].x, 2) + pow(G[i].y, 2) <= pow((7.5 + D), 2);
 70     return a;
 71 }
 72 
 73 bool jump(int i, int j)
 74 {
 75     return pow(G[i].x - G[j].x, 2) + pow(G[i].y - G[j].y, 2) <= D * D;
 76 }
 77 
 78 bool toBank(int i)
 79 {
 80     int x = G[i].x, y = G[i].y;
 81     return (x <= D - 50 || x >= 50 - D || y <= D - 50 || y >= 50 - D);
 82 }
 83 
 84 bool shorter(vector<int> path1, vector<int> path2)
 85 {
 86     if (path1.size() != path2.size())
 87         return path1.size() < path2.size();
 88     else {
 89         int a = path1[path1.size() - 1];
 90         int b = path2[path2.size() - 1];
 91         return pow(G[a].x, 2) + pow(G[a].y, 2) <= pow(G[b].x, 2) + pow(G[b].y, 2);
 92     }
 93 }
 94 
 95 bool bfs(int s, vector<int>& p)
 96 {
 97     queue q;
 98     enQueue(s, q);
 99     bool marked[100] = {};
100     int pathTo[100];
101     marked[s] = true;
102     pathTo[s] = -1;
103 
104     bool success = false;
105     int v, w;
106     while (!isEmpty(q))
107     {
108         v = deQueue(q);
109         if (toBank(v)) //可以到岸边
110         {
111             success = true;
112             break;
113         }
114         for (w = 0; w < N; w++)
115         {
116             if (!marked[w] && jump(v, w))
117             {
118                 enQueue(w, q);
119                 marked[w] = true;
120                 pathTo[w] = v;
121             }
122         }
123     }
124 
125     if (!success) return false;
126     vector<int> vec;
127     while (v != -1)
128     {
129         vec.push_back(v);
130         v = pathTo[v];
131     }
132     p = vec;
133     return true;
134 }
135 
136 void enQueue(int i, queue& q)
137 {
138     q.tail = (q.tail + 1) % 100;
139     q.arr[q.tail] = i;
140 }
141 
142 int deQueue(queue& q)
143 {
144     q.head = (q.head + 1) % 100;
145     return q.arr[q.head];
146 }
147 
148 bool isEmpty(queue q)
149 {
150     return q.head == q.tail;
151 }