UVA 10047The Monocycle（BFS）

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题目链接：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=988

题意：从S走到T，每走一格车轮转一个颜色，求到T时车轮颜色为绿色（起始也为绿色）的最短路径。每次可向当前车轮方向走一格，或者原地向左转动或向右转动。

思路：几乎也为裸的BFS，多记录一些状态，即需要记录到某点车轮为某个方向某个颜色时的最短路径。

代码：

#include <stdio.h>#include <string.h>#include <iostream>#include <algorithm>#include <math.h>#include <queue>using namespace std;const int N = 40;const int INF = 0x3f3f3f3f;struct Node {  int x, y;  int color, step, turn;};char _map[N][N];int n, m;int dis[N][N][10][10];int x[4] = {-1, 0, 1, 0};int y[4] = {0, 1, 0, -1};bool pass(Node to) {  if (to.x >= 0 && to.x < n && to.y >= 0 && to.y < m && _map[to.x][to.y] != '#'    && dis[to.x][to.y][to.color][to.turn] > to.step)    return true;  return false;}int bfs(Node s) {  memset(dis, INF, sizeof(dis));  queue<Node> q;  q.push(s);  dis[s.x][s.y][s.color][s.turn] = s.step;  while (!q.empty()) {    Node now = q.front();    q.pop();    if (_map[now.x][now.y] == 'T' && now.color == 0) {      return now.step;    }    Node to;    to.x = now.x;    to.y = now.y;    to.color = now.color;    to.step = now.step + 1;    to.turn = (now.turn + 1) % 4;    if (pass(to)) {      q.push(to);      dis[to.x][to.y][to.color][to.turn] = to.step;    }    to.turn = (now.turn + 3) % 4;    if (pass(to)) {      q.push(to);      dis[to.x][to.y][to.color][to.turn] = to.step;    }    to.x = now.x + x[now.turn];    to.y = now.y + y[now.turn];    to.color = (now.color + 1) % 5;    to.turn = now.turn;    if (pass(to)) {      q.push(to);      dis[to.x][to.y][to.color][to.turn] = to.step;    }  }  return -1;}int main() {  int i_case = 1;  while (scanf("%d%d", &n, &m) != EOF) {    if (!n && !m)      break;    for (int i = 0; i < n; i++)      scanf("%s", _map[i]);    Node st;    for (int i = 0; i < n; i++) {      for (int j = 0; j < m; j++)  {        if (_map[i][j] == 'S') {          st.x = i, st.y = j;          st.turn = 0;          st.color = 0;          st.step = 0;        }      }    }    int res = bfs(st);    if (i_case > 1)      printf("\n");    if (res == -1)      printf("Case #%d\ndestination not reachable\n", i_case++);    else      printf("Case #%d\nminimum time = %d sec\n", i_case++, res);  }  return 0;}

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