ZOJ 1005 解题报告

ZOJ 1005 解题报告

BFS+剪枝.所谓的剪枝就是如果A为空的时候不能进行"empty A"的操作等.
PS:也可利用A和B的互质性解决,在此用搜索主要是想多练习一下搜索的代码.

Code
  1#include <iostream>
  2#include <string>
  3#include <queue>
  4using namespace std;
  5
  6const string description[7] = 
  7{
  8    "",
  9    "fill A",
 10    "fill B",
 11    "empty A",
 12    "empty B",
 13    "pour A B",
 14    "pour B A"
 15};
 16
 17enum Action
 18{
 19    NONE = 0,
 20    FILL_A,
 21    FILL_B,
 22    EMPTY_A,
 23    EMPTY_B,
 24    POUR_A_B,
 25    POUR_B_A
 26};
 27
 28struct State
 29{
 30    int A;
 31    int B;
 32    State * LastState;
 33    Action LastAction;
 34
 35    bool operator==(const State & state) const
 36    {
 37        return A == state.A && B == state.B;
 38    }
 39};
 40
 41bool IsVisit(State * state, vector<State *> & states)
 42{
 43    vector<State *>::iterator ite = states.begin();
 44    vector<State *>::iterator end = states.end();
 45    while(ite != end)
 46    {
 47        if(*state == *(*ite))
 48            return true;
 49        ++ite;
 50    }
 51    return false;
 52}
 53
 54bool IsSuccess(const State * state, int goal)
 55{
 56    return state->B == goal;
 57}
 58
 59void StoreState(State * last_state, State * state, vector<State *> & visited, queue<State *> & q, Action action)
 60{
 61    if(!IsVisit(state, visited))
 62    {
 63        state->LastState = last_state;
 64        state->LastAction = action;
 65        q.push(state);
 66        visited.push_back(state);
 67    }
 68}
 69
 70int _tmain(int argc, _TCHAR* argv[])
 71{
 72    int A, B, goal;
 73    vector<State *> visited;
 74    queue<State *> q;
 75    while(cin >> A >> B >> goal)
 76    {
 77        State * empty_state = new State();
 78        State * next_state;
 79        empty_state->A = empty_state->B = 0;
 80        empty_state->LastAction = NONE;
 81        visited.push_back(empty_state);
 82        q.push(empty_state);
 83
 84        while(!q.empty())
 85        {
 86            State * current_state = q.front();
 87            q.pop();
 88
 89            // Fill A
 90            if(current_state->A < A)
 91            {
 92                next_state = new State();
 93                next_state->A = A;
 94                next_state->B = current_state->B;
 95                StoreState(current_state, next_state, visited, q, FILL_A);
 96                if(IsSuccess(next_state, goal))
 97                    break;
 98            }
 99            // Fill B
100            if(current_state->B < B)
101            {
102                next_state = new State();
103                next_state->A = current_state->A;
104                next_state->B = B;
105                StoreState(current_state, next_state, visited, q, FILL_B);
106                if(IsSuccess(next_state, goal))
107                    break;
108            }
109            // Empty A
110            if(current_state->A != 0)
111            {
112                next_state = new State();
113                next_state->A = 0;
114                next_state->B = current_state->B;
115                StoreState(current_state, next_state, visited, q, EMPTY_A);
116                if(IsSuccess(next_state, goal))
117                    break;
118            }
119            // Empty B
120            if(current_state->B != 0)
121            {
122                next_state = new State();
123                next_state->A = current_state->A;
124                next_state->B = 0;
125                StoreState(current_state, next_state, visited, q, EMPTY_B);
126                if(IsSuccess(next_state, goal))
127                    break;
128            }
129            // Pour A B
130            if(current_state->A != 0 && current_state->B != B)
131            {
132                next_state = new State();
133                int diff = B - current_state->B;
134                int poured = min(current_state->A, diff);
135                next_state->B = current_state->B + poured;
136                next_state->A = current_state->A - poured;
137                StoreState(current_state, next_state, visited, q, POUR_A_B);
138                if(IsSuccess(next_state, goal))
139                    break;
140            }
141            // Pour B A
142            if(current_state->B != 0 && current_state->A != A)
143            {
144                next_state = new State();
145                int diff = A - current_state->A;
146                int poured = min(current_state->B, diff);
147                next_state->A = current_state->A + poured;
148                next_state->B = current_state->B - poured;
149                StoreState(current_state, next_state, visited, q, POUR_B_A);
150                if(IsSuccess(next_state, goal))
151                    break;
152            }
153        }
154
155        vector<Action> action_list;
156        State * temp_state = next_state;
157        while(temp_state->LastAction != NONE)
158        {
159            action_list.push_back(temp_state->LastAction);
160            temp_state = temp_state->LastState;
161        }
162
163        vector<Action>::reverse_iterator r_ite = action_list.rbegin();
164        vector<Action>::reverse_iterator r_end = action_list.rend();
165        while(r_ite != r_end)
166        {
167            cout << description[(int)(*r_ite)] << endl;
168            ++r_ite;
169        }
170        cout << "success" << endl;
171
172        delete empty_state, next_state;
173        visited.clear();
174        while(!q.empty())
175            q.pop();
176    }
177
178    return 0;
179}
180
181