HDU 1428 漫步校园（Spfa+记忆化搜索）

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#include<iostream>#include<algorithm>#include<cstring>#include<string>#include<sstream>#include<queue>using namespace std;typedef long long LL;const int M = 10000;const int INF = 0x3f3f3f3f;int n;int dir[][2] = { 1,0,-1,0,0,-1,0,1 };int mp[55][55];int s[55][55];bool vis[55][55];LL dp[55][55];struct node{int x, y;}st, nx;queue<node >q;void bfs()      //记录每个点到终点的最短路{for (int i = 1; i <= n; ++i){for (int j = 1; j <= n; ++j){s[i][j] = INF;}}memset(vis, 0, sizeof(vis));vis[n][n] = 1;s[n][n] = mp[n][n];    //由于题目要求 需要逆向更新 node st;st.x = n;st.y = n;q.push(st);node tmp;while (!q.empty())  {node nx = q.front();q.pop();int x = nx.x;int y = nx.y;vis[x][y] = 0;for (int i = 0; i <4; ++i){int xx = x + dir[i][0];int yy = y + dir[i][1];if (xx<1 || xx>n || yy<1 || yy>n)continue;if (s[xx][yy]>s[x][y] + mp[xx][yy]){s[xx][yy] = s[x][y] + mp[xx][yy];if (!vis[xx][yy]){tmp.x = xx;tmp.y = yy;q.push(tmp);vis[xx][yy] = 1;}}}}return;}LL dfs(int x, int y){if (x == n && y == n)return 1;LL ans = 0;if (!dp[x][y]){for (int i = 0; i < 4; ++i){int xx = x + dir[i][0];int yy = y + dir[i][1];if (xx >= 1 && xx <= n && yy >= 1 && yy <= n && s[xx][yy] < s[x][y]){ans += dfs(xx, yy);}}dp[x][y] = ans;}return dp[x][y];}int main(){while (~scanf("%d", &n)){for (int i = 1; i <= n; ++i){for (int j = 1; j <= n; ++j){scanf("%d", &mp[i][j]);}}//memset(s, 0, sizeof(s));bfs();memset(dp, 0, sizeof(dp));cout << dfs(1, 1) << endl;}return 0;}

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