CF 廣搜（基礎）

1 2
.#...
.#.#.
...#.

output

15

input

3 3
4 5
..#
.#.
#..

output

IMPOSSIBLE

http://codeforces.com/gym/100796/problem/D

題目大意：

剛開始是在小鎮裏面，小鎮到荒地要a元，荒地到小鎮要b元。問，怎麼走才能花費的最少

思路：

基礎的廣搜。。。不過我要吐槽。。。爲啥我第一種方法是wa了，害我重新又寫了好一會兒TAT

#include
#include
#include
#include

using namespace std;

typedef long long ll;
typedef pair P;
const int maxn = 500 + 5;
int n, m;
int a, b;
char atlas[maxn][maxn];
int step[maxn][maxn];
int dx[4] = {1, 0, 0, -1};
int dy[4] = {0, 1, -1, 0};
int val[maxn][maxn];

void init(){
    memset(step, 0, sizeof(step));
    memset(atlas, 0, sizeof(atlas));
    memset(val, -1, sizeof(val));
    memset(step, -1, sizeof(step));
    scanf("%d%d", &a, &b);
    for (int i = 0; i < m; i++){
        scanf("%s", atlas[i]);
    }
    val[0][0] = a;
    queue 

que; que.push(make_pair(0, 0)); while (!que.empty()){ P tmp = que.front(); que.pop(); for (int i = 0; i <= 3; i++){ int x = tmp.first + dx[i]; int y = tmp.second + dy[i]; if (x < 0 || y < 0 || x >= m || y >= n) continue; if (atlas[x][y] == '#' || atlas[x][y] == '\0') continue; if (val[x][y] != -1) continue; if (val[tmp.first][tmp.second] == a){ val[x][y] = b; } else val[x][y] = a; que.push(make_pair(x, y)); } } /* printf("check\n"); for (int i = 0; i < m; i++){ for (int j = 0; j < n; j++){ printf("%d ", val[i][j]); } printf("\n"); } */ } ll bfs(){ queue

que; que.push(make_pair(0, 0)); step[0][0] = 0; while (!que.empty()){ P tmp = que.front(); que.pop(); for (int i = 0; i < 4; i++){ int x = tmp.first + dx[i]; int y = tmp.second + dy[i]; if (x < 0 || y < 0 || x >= m || y >= n) continue; if (atlas[x][y] == '#' || atlas[x][y] == '\0') continue; if (step[x][y] != -1) continue; step[x][y] = step[tmp.first][tmp.second] + val[x][y]; //printf("step[%d][%d] = %d\n", x, y, step[x][y]); que.push(make_pair(x, y)); } } if (step[m-1][n-1] == -1) printf("IMPOSSIBLE\n"); else printf("%d\n", step[m-1][n-1]); } int main(){ while (scanf("%d%d", &n, &m) == 2){ init(); bfs(); } return 0; }