graph

Author: tjd229

oj/NOI18_citymapping/citymapping.cpp

@@ -0,0 +1,81 @@
+//graph
+
+#include "citymapping.h"
+#include <vector>
+#include <algorithm>
+#define ll long long
+#define pii pair<int,int>
+#define pli pair<ll,int>
+using namespace std;
+vector<pii > edge[1001];
+int sz[1001], p[1001];
+ll d[1001][1001];
+int dfs(int x) {
+	if (edge[x].empty()) return x;
+	int mx = 0;
+	int nxt = 0;
+	for (auto p : edge[x]) {
+		int c = p.first;
+		if (mx < sz[c]) {
+			nxt = c;
+			mx = sz[c];
+		}
+	}
+	return dfs(nxt);
+}
+int find_par(int root, int x, ll dist) {
+	//printf("%d,%d,%lld\n",root,x,dist);
+	if (edge[root].empty()) return root;
+
+	int leaf = dfs(root);
+	ll x2l = get_distance(x, leaf);
+	int lca = leaf;
+	while (d[root][leaf] + dist < (d[root][lca] << 1) + x2l)
+		lca = p[lca];// , printf("%d", lca);
+	if (edge[lca].size() <= 1) return lca;
+	//2
+	int l = edge[lca][0].first, r = edge[lca][1].first;
+	if (sz[l] < sz[r]) return find_par(l, x, dist - d[root][l]);
+	else return find_par(r, x, dist - d[root][r]);
+}
+void find_roads(int N, int Q, int A[], int B[], int W[]) {
+	ll mx = 0;
+	int root = 0;
+	for (int i = 2; i <= N; ++i) {
+		d[1][i] = d[i][1] = get_distance(1, i);
+		if (d[1][i] > mx) {
+			mx = d[1][i];
+			root = i;
+		}
+	}
+	vector<pli > v;
+	for (int i = 1; i <= N; ++i) {
+		if (i == root) continue;
+		d[root][i] = d[i][root] = get_distance(root, i);
+		v.push_back({ d[root][i],i });
+	}
+	sort(v.begin(), v.end());
+	sz[root] = 1;
+	for (auto pr : v) {
+		
+		int x = pr.second;
+		ll dist = pr.first;
+		int par = find_par(root, x, dist);
+		edge[par].push_back({ x,dist - d[par][root] });
+		p[x] = par; sz[x] = 1;
+		while (par) {
+			++sz[par];
+			d[par][x] = d[x][par] = d[root][x] - d[root][par];
+			par = p[par];
+		}
+	}
+	int len = 0;
+	for (int i = 1; i <= N; ++i) {
+		for (auto p : edge[i]) {
+			A[len] = i;
+			B[len] = p.first;
+			W[len] = p.second;
+			++len;
+		}
+	}
+}