hrbust 1621 迷宫问题II 广搜

// hrbust 1621 迷宫问题II
// 优先队列——广搜
// 什么时候需要回溯什么时候不需要？

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <queue>
using namespace std;
#define maxn 100000

char mp[210][210];
int dir[4][2] = {1, 0, -1, 0, 0, 1, 0, -1};
int vis[210][210];
int r, c;
int step[210][210];
int stx, sty, edx, edy;

bool check(int x, int y) {
if (x >= 0 && x < r && y >= 0 && y < c && !vis[x][y] && mp[x][y] != '#')
return true;
return false;
}

struct Node {
friend bool operator < (Node n1, Node n2)
{
return step[n1.x][n1.y] > step[n2.x][n2.y];//"<"为从大到小排列，">"为从小打到排列
}
int x, y;
}node[40100];

priority_queue<Node> qn;

void bfs(int x, int y) {
int head = 0, tail = 0;
memset(vis, 0, sizeof(vis));
for (int i=0; i<r; ++i) {
for (int j=0; j<c; ++j) {
step[i][j] = maxn;
}
}
while(!qn.empty()) {
qn.pop();
}

vis[x][y] = 1;
step[x][y] = 0;
Node temp;
temp.x = x;
temp.y = y;
// node[tail++] = temp;
qn.push(temp);
//while(head < tail) {
while(!qn.empty()) {
//Node now = node[head++];
Node now = qn.top();
qn.pop();
for (int i=0; i<4; ++i) {
temp.x = now.x + dir[i][0];
temp.y = now.y + dir[i][1];
int tstep = 0;
if (check(temp.x, temp.y)) {
if (mp[temp.x][temp.y] >= '1' && mp[temp.x][temp.y] <= '9')
tstep = mp[temp.x][temp.y] - '0' + 1;
else tstep = 1;
step[temp.x][temp.y] = min(step[temp.x][temp.y], step[now.x][now.y] + tstep);
vis[temp.x][temp.y] = 1;
//node[tail++] = temp;
qn.push(temp);
if (temp.x == edx && temp.y == edy) break;
}
}
}
return;
}

int main() {
int t;
cin >> t;
while(t--) {
cin >> r >> c;

for (int i=0; i<r; ++i) {
for (int j=0; j<c; ++j) {
cin >> mp[i][j];
if (mp[i][j] == 'Z') {
stx = i, sty = j;
}
else if (mp[i][j] == 'W') {
edx = i, edy = j;
}
}
}

bfs(stx, sty);
int ans = step[edx][edy];
if (ans == maxn) {
cout << "IMPOSSIBLE\n";
}
else cout << ans << endl;
}
return 0;
}