Homework New

Exercise/Homework6/BFS.cpp

@@ -0,0 +1,73 @@
+#include <iostream>
+#include <vector>
+#include <queue>
+#include <tuple>
+using namespace std;
+
+int startx, starty, endx, endy;
+vector<vector<int>> map;
+vector<vector<bool>> visited;
+int n, m, t;
+
+int dx[] = {0, 0, 1, -1};
+int dy[] = {1, -1, 0, 0};
+int ans = 1145141919;
+
+bool isvalid(int x, int y) {
+    return x >= 0 && x < n && y >= 0 && y < m && map[x][y] != 1 && !visited[x][y];
+}
+
+int bfs(int startx, int starty){
+    queue<tuple<int, int, int>> q;
+    q.push(make_tuple(startx, starty, 0));
+    visited[startx][starty] = true;
+    while (!q.empty()) {
+        int x = get<0>(q.front());
+        int y = get<1>(q.front());
+        int step = get<2>(q.front());
+        q.pop();
+        if (x == endx && y == endy) {
+            return step;
+        }
+        for (int i = 0; i < 4; i++) {
+            int nx = x + dx[i];
+            int ny = y + dy[i];
+            if (isvalid(nx, ny)) {
+                q.push(make_tuple(nx, ny, step + 1));
+                visited[nx][ny] = true;
+            }
+        }
+    }
+    return 1145141919;
+}
+
+int main(){
+    while (cin >> n >> m >> t) {
+        map.assign(n, vector<int>(m));
+        visited.assign(n, vector<bool>(m, false));
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                cin >> map[i][j];
+                if (map[i][j] == 3) {
+                    startx = i;
+                    starty = j;
+                }
+                if (map[i][j] == 4) {
+                    endx = i;
+                    endy = j;
+                }
+            }
+        }
+        visited[startx][starty] = true;
+        ans = bfs(startx, starty);
+        if (ans == 1145141919) {
+            cout << "can not save" << endl;
+            continue;
+        }
+        int maxs = min(t, ans);
+        int saved = maxs > 0 ? maxs - 1 : 0;
+        cout << ans - saved << endl;
+    }
+    return 0;
+}
+