UVA 589 - Pushing Boxes（BFS+状态判重）

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题目链接：589 - Pushing Boxes

题意：就是模拟推箱子游戏，要求推箱子次数最少，然后是总次数最少的方案。

思路：广搜+状态判重，用人的位置和箱子位置和当前步数作为状态。然后由于是要优先推箱子次数少，所以利用优先队列去取状态。

代码：

#include <stdio.h>#include <string.h>#include <iostream>#include <vector>#include <queue>#include <string>#include <map>#define INF 0x3f3f3f3fusing namespace std;const int d[4][2] = {{-1, 0}, {1, 0}, {0, 1}, {0, -1}};const char s1[10] = "NSEW";const char s2[10] = "nsew";const int N = 25;int r, c, push_num;char g[N][N];string ans;map<int, bool> vis[20][20][20][20];typedef pair<int, int> pi;pi s, b, t;struct State {int sx, sy, bx, by, num;string path;State() {}State(int _sx, int _sy, int _bx, int _by, int _num) {sx = _sx; sy = _sy; bx = _bx; by = _by; num = _num;path = "";}friend bool operator < (State a, State b) {if (a.num != b.num)return a.num > b.num;return a.path.length() > b.path.length();}};void init() {ans = "";push_num = INF;for (int i = 0; i < r; i++) {scanf("%s", g[i]);for (int j = 0; j < c; j++) {if (g[i][j] == 'S')s = make_pair(i, j);else if (g[i][j] == 'B')b = make_pair(i, j);else if (g[i][j] == 'T')t = make_pair(i, j);if (g[i][j] != '#')g[i][j] = '.';for (int k = 0; k < r; k++)for (int l = 0; l < c; l++)vis[i][j][k][l].clear();}}}bool check(int x, int y) {if (x < 0 || x >= r || y < 0 || y >= c || g[x][y] != '.') return false;return true;}void solve() {priority_queue<State> Q;vis[s.first][s.second][b.first][b.second][0] = 1;Q.push(State(s.first, s.second, b.first, b.second, 0));while (!Q.empty()) {State p = Q.top();Q.pop();if (p.bx == t.first && p.by == t.second) {if (push_num > p.num) {ans = p.path;push_num = p.num;} else if (push_num == p.num) {if (ans.length() > p.path.length())ans = p.path;}else break;continue;}for (int i = 0; i < 4; i++) {State q = p;q.sx += d[i][0];q.sy += d[i][1];if (!check(q.sx, q.sy)) continue; q.path += s2[i];if (q.sx == q.bx && q.sy == q.by) {q.bx += d[i][0], q.by += d[i][1];if (!check(q.bx, q.by)) continue;q.num++;if (q.num > push_num) continue;q.path[q.path.length() - 1] = s1[i];}if (vis[q.sx][q.sy][q.bx][q.by][ans.length()]) continue;vis[q.sx][q.sy][q.bx][q.by][ans.length()] = true;Q.push(q);}}}int main() {int cas = 0;while (~scanf("%d%d", &r, &c) && r || c) {init();printf("Maze #%d\n", ++cas);solve();if (ans.length())cout << ans << endl;else printf("Impossible.\n");printf("\n");}return 0;}

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