Add variations on PDP26 A task (juniors, graphs)

2014/pdp26-a-bfs.cpp

+#include <stdio.h>
+#include <vector>
+#include <queue>
+
+using namespace std;
+
+enum state { UNVISITED, SEEN, VISITED };
+
+int main ()
+{
+  int N, M;
+  scanf("%d %d", &N, &M);
+
+  vector<int> neighbors[N+1];
+
+  for (int i=0; i<M; i++) {
+    int u, v;
+    scanf("%d %d", &u, &v);
+    neighbors[u].push_back(v);
+    neighbors[v].push_back(u);
+  }
+
+  // BFS scanning from 1
+  queue<int> Q;
+  vector<int> p(N+1);
+  vector<state> m(N+1);
+  Q.push(1);
+  m[1] = SEEN;
+  while (!Q.empty()) {
+    int u = Q.front();
+    Q.pop();
+    m[u] = VISITED;
+#if 0
+    for (vector<int>::iterator i = neighbors[u].begin();
+         i != neighbors[u].end(); i++)
+      if (m[*i] == UNVISITED) {
+        Q.push(*i);
+        m[*i] = SEEN;
+        p[*i] = u;
+      }
+#else
+    for (int k=0; k < neighbors[u].size(); k++) {
+      int v = neighbors[u][k];
+      if (m[v] == UNVISITED) {
+        Q.push(v);
+        m[v] = SEEN;
+        p[v] = u;
+      }
+    }
+#endif
+  }
+
+  for (int i=1; i<=N; i++)
+    printf("parent of %d is %d\n", i, p[i]);
+  
+  return 0;
+}

2014/pdp26-a-dfs.cpp

+#include <stdio.h>
+#include <vector>
+#include <queue>
+
+using namespace std;
+
+vector< vector<int> > neighbors;
+vector<int> p;
+enum state { UNVISITED, SEEN, VISITED };
+vector<state> m;
+
+void dfs (int u)
+{
+  m[u] = SEEN;
+  for (vector<int>::iterator i = neighbors[u].begin();
+       i != neighbors[u].end(); i++)
+    if (m[*i] == UNVISITED) {
+      p[*i] = u;
+      dfs(*i);
+    }
+  m[u] = VISITED;
+}
+
+int main ()
+{
+  int N, M;
+  scanf("%d %d", &N, &M);
+
+  neighbors.resize(N+1);
+
+  for (int i=0; i<M; i++) {
+    int u, v;
+    scanf("%d %d", &u, &v);
+    neighbors[u].push_back(v);
+    neighbors[v].push_back(u);
+  }
+
+  // DFS scanning from all possible starts
+  p.resize(N+1);
+  m.resize(N+1);
+  for (int i=1; i<=N; i++)
+    if (m[i] == UNVISITED)
+      dfs(i);
+
+  for (int i=1; i<=N; i++)
+    printf("parent of %d is %d\n", i, p[i]);
+  
+  return 0;
+}

2014/pdp26-a-list.cpp

+#include <stdio.h>
+#include <vector>
+
+using namespace std;
+
+int main ()
+{
+  int N, M;
+  scanf("%d %d", &N, &M);
+
+  // you don't really need an adjacency list for
+  // this problem!!!
+  vector<int> neighbors[N];
+
+  for (int i=0; i<M; i++) {
+    int u, v;
+    scanf("%d %d", &u, &v);
+    u--; v--;
+    neighbors[u].push_back(v);
+    neighbors[v].push_back(u);
+  }
+
+  int count = 0;
+  for (int i=0; i<N; i++)
+    if (neighbors[i].size() < 2) count++;
+  printf("%d\n", count);
+  
+  return 0;
+}

2014/pdp26-a-matrix.cpp

+#include <stdio.h>
+#include <vector>
+
+using namespace std;
+
+int main ()
+{
+  int N, M;
+  scanf("%d %d", &N, &M);
+
+  // we should not really be using an adjacency
+  // matrix for this problem!!!
+  vector<bool> A[N];
+  for (int i=0; i<N; i++)
+    A[i].resize(N);
+
+  for (int i=0; i<M; i++) {
+    int u, v;
+    scanf("%d %d", &u, &v);
+    u--; v--;
+    A[u][v] = A[v][u] = true;
+  }
+
+  int count = 0;
+  for (int i=0; i<N; i++) {
+    int degree_i = 0;
+    for (int j=0; j<N; j++)
+      if (A[i][j]) degree_i++;
+    if (degree_i < 2) count++;
+  }
+  printf("%d\n", count);
+  
+  return 0;
+}