UVA - 11624 Fire!（15.10.10 搜索专题）bfs

来源：互联网发布：鹰眼图js 编辑：程序博客网时间：2024/06/05 10:13

题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=28833

题意：joe在图中，图中有几个起火点，火以没分钟每格的速度蔓延，Joe的移动速度也是每分钟每格，问Joe有没有可能从火场逃生，跑出图。

思路：先对每个起火点bfs，求出图中各个点起火的时间（最早的时间），然后在对Joe来bfs，注意已经起火的地方是不能走的。

#include<iostream>#include<cstdio>#include<cstring>#include<queue>#include<climits>using namespace std;#define inf 0x3f3f3fconst int dirx[4] = { 0, 0, 1, -1 };const int diry[4] = { 1, -1, 0, 0 };char map[1010][1010];bool vis[1010][1010];int disFire[1010][1010];int disPeo[1010][1010];int r, c;struct Point{int x, y;Point(int xx, int yy) :x(xx), y(yy){}Point(){}};Point posFire[100010];int numOfFire;Point posJoe;void bfsFire(int x,int y){queue<Point>que;que.push(Point(x, y));disFire[x][y] = 0;while (!que.empty()){Point loc = que.front();que.pop();for (int i = 0; i < 4; i++){int xx = loc.x + dirx[i];int yy = loc.y + diry[i];if (xx >= 0 && xx < r && yy >= 0 && yy<c && map[xx][yy] == '.'&& disFire[xx][yy]>disFire[loc.x][loc.y] + 1){que.push(Point(xx, yy));disFire[xx][yy] = disFire[loc.x][loc.y] + 1;}}}}int bfsPeo(int x, int y){queue<Point>que;que.push(Point(x, y));disPeo[x][y] = 0;vis[x][y] = true;while (!que.empty()){Point loc = que.front();que.pop();if (loc.x == 0 || loc.y == 0 || loc.x == r - 1 || loc.y == c - 1)return disPeo[loc.x][loc.y]+1;for (int i = 0; i < 4; i++){int xx = loc.x + dirx[i];int yy = loc.y + diry[i];if (xx >= 0 && xx < r && yy >= 0 && yy<c && map[xx][yy] == '.'&& disFire[xx][yy]>disPeo[loc.x][loc.y]+1 && !vis[xx][yy]){que.push(Point(xx, yy));disPeo[xx][yy] = disPeo[loc.x][loc.y] + 1;vis[xx][yy] = true;}}}return -1;}int main(){int casen;cin >> casen;while (casen--){cin >> r >> c;for (int i = 0; i < r; i++)cin >> map[i];numOfFire = 0;for (int i = 0; i < r; i++)for (int j = 0; j < c; j++){if (map[i][j] == 'F'){posFire[numOfFire].x = i;posFire[numOfFire++].y = j;}else if (map[i][j] == 'J'){posJoe.x = i;posJoe.y = j;}}memset(disFire, inf, sizeof(disFire));memset(disPeo, inf, sizeof(disPeo));memset(vis, false, sizeof(vis));for (int i = 0; i < numOfFire; i++){int x = posFire[i].x;int y = posFire[i].y;bfsFire(x, y);}int ans = bfsPeo(posJoe.x, posJoe.y);if (ans == -1) cout << "IMPOSSIBLE" << endl;else cout << ans << endl;}}

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