update

poj/1724.roads/main.cc

@@ -0,0 +1,61 @@
+#include <cstdio>
+#include <cstring>
+#include <vector>
+
+using namespace std;
+
+const int K = 10000, R = 10000;
+const int N = 100, L = 100, T = 100;
+const int INF = 1 << 30;
+
+int k, n, r, min_l;
+
+// Save intermediate results for pruning,
+// mid_l[i][j] means the min len at city i with coin j.
+int mid_l[N + 1][K + 1];
+bool flag[N + 1];
+
+struct Path {
+  int dst;
+  int len;
+  int cst;
+  Path(int d, int l, int c) : dst(d), len(l), cst(c) {}
+};
+
+vector<Path> adj[N + 1];
+
+void dfs(int i, int p, int coin) {
+  if (i == n) {
+    min_l = min(min_l, p);
+    return;
+  }
+  if (min_l <= p) return;
+  if (mid_l[i][coin] <= p)
+    return;
+  else
+    mid_l[i][coin] = p;
+  flag[i] = true;
+  vector<Path> &vec = adj[i];
+  for (int j = 0; j < vec.size(); j++) {
+    if (flag[vec[j].dst] || coin < vec[j].cst) continue;
+    dfs(vec[j].dst, p + vec[j].len, coin - vec[j].cst);
+  }
+  flag[i] = false;
+};
+
+int main() {
+  scanf("%d %d %d", &k, &n, &r);
+  for (int i = 0, s, d, l, t; i < r; i++) {
+    scanf("%d %d %d %d", &s, &d, &l, &t);
+    adj[s].push_back(Path(d, l, t));
+  }
+  min_l = INF;
+  memset(flag, 0, sizeof(flag));
+  memset(mid_l, 0x3F, sizeof(mid_l));
+  dfs(1, 0, k);
+  if (min_l == INF)
+    printf("-1\n");
+  else
+    printf("%d\n", min_l);
+  return 0;
+}