嗯...
题目链接：https://www.luogu.org/problem/P3956
这是一道比较好搜的题，注意一些剪枝、预处理和魔法的处理问题（回溯）。
AC代码：
1 #include<cstdio> 2 #include<cstring> 3 #include<iostream> 4 5 using namespace std; 6 7 int n, m, ans = 0x7ffffff; 8 int dir[4][2] = {{1, 0}, {-1, 0}, {0, -1}, {0, 1}}; 9 int mp[110][110], dp[110][110]; 10 11 inline void dfs(int x, int y, int sum, bool magic){ 12 if(x < 1 || y < 1 || x > m || y > m) return; 13 if(sum >= dp[x][y]) return;//记忆化剪枝 14 dp[x][y] = sum; 15 if(x == m && y == m) {ans = min(ans, sum); return;} 16 for(int i = 0; i < 4; i++){ 17 int nx = x + dir[i][0]; 18 int ny = y + dir[i][1]; 19 if(nx < 1 || ny < 1 || nx > m || ny > m) continue; 20 if(mp[nx][ny]){ 21 if(mp[x][y] == mp[nx][ny]) dfs(nx, ny, sum, 0); 22 else dfs(nx, ny, sum+1, 0); 23 } 24 else{ 25 if(!magic){ 26 mp[nx][ny] = mp[x][y]; 27 dfs(nx, ny, sum+2, 1); 28 mp[nx][ny] = 0; 29 }//处理魔法，注意回溯 30 } 31 } 32 } 33 34 int main(){ 35 memset(dp, 0x3f3f3f, sizeof(dp)); 36 scanf("%d%d", &m, &n); 37 for(int i = 1; i <= n; i++){ 38 int x, y, c; 39 scanf("%d%d%d", &x, &y, &c); 40 mp[x][y] = c + 1; 41 //无色-0 42 } 43 dfs(1, 1, 0, 0); 44 printf("%d", ans == 0x7ffffff ? -1 : ans); 45 return 0; 46 }