[算法] BFS ： poj 2312 Battle City 示例

纪念第一次用  “优先队列”， 第一次知道 “方向数组” ！ BFS ： 谁出队就找谁的邻接点访问之并入队！

#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <vector>
#include <stack>
#include <deque>
#include <queue>
#include <bitset>
#include <list>
#include <map>
#include <set>
#include <iterator>
#include <algorithm>
#include <functional>
#include <utility>
#include <sstream>
#include <climits>
#include <cassert>
#define BUG puts("here!!!");

using namespace std;
const int N = 305;
struct Point {
	int x, y;
	int steps;
};
char mmap[N][N];
int n, m;
int dx[] = {0, 0, -1, 1};
int dy[] = {-1, 1, 0, 0};
bool ok(int x, int y) {
	return (x >= 0 && x < m && y >= 0 && y < n);
}
Point you, tag;
bool operator < (const Point &a, const Point &b) {
	return a.steps > b.steps;
}
int bfs() {
    priority_queue<Point> Q;
	Q.push(you);
	Point t, tmp;
	int xx, yy;
	while(!Q.empty()) {
		t = Q.top(); Q.pop();
		for(int i = 0; i < 4; i++) {
			xx = t.x + dx[i];
			yy = t.y + dy[i];
			if(!ok(xx, yy) || mmap[xx][yy] == 'R' || mmap[xx][yy] == 'S') {
				continue;
			}
			if(xx == tag.x && yy == tag.y) return t.steps + 1;
			tmp.x = xx;
		    tmp.y = yy;
			if(mmap[xx][yy] == 'B') {
				tmp.steps = t.steps + 2;
			}
			else tmp.steps = t.steps + 1;
			mmap[xx][yy] = 'R';
			Q.push(tmp);
		}
	}
	return -1;
}
int main() {
	while(scanf("%d%d", &m, &n), m|n) {
		for(int i = 0; i < m; i++) {
			for(int j = 0; j < n; j++) {
				cin >> mmap[i][j];
				if(mmap[i][j] == 'Y') {
					you.x = i;
					you.y = j;
					you.steps = 0;
				}
				else if(mmap[i][j] == 'T') {
					tag.x = i, tag.y = j;
				}
			}
		}
		printf("%d\n", bfs());
	}
	return 0;
}