Zoj 3820 4acm/ICPC Mudanjiang Division B

3797714 2014-10-12: 19 accepted 3820 C ++ 1350 70240zz_1215
A troublesome question. At the beginning, the segment exception is not stopped. Later I knew it was a stack explosion, and then I used an array to simulate recursion.

The idea is quite simple. First find the diameter of the tree and take it out separately. It can prove that the last two points must be on the diameter. I will not prove it.

Then, find the maximum extended distance of each point in the diameter.

Perform rmq twice for this distance. The first time is to calculate the maximum distance to the left. Therefore, the sequence of this distance must be + 1, + 2, + 3 ....... + n-1, + n

The second is for calculating the maximum distance to the right, so the sequence must be + N, + n-1... + 3, + 2, + 1

Then determine a left start point and a right start point.

The final complexity is O (n * log (n ))

The implementation is still quite complicated.

Finally, I would like to remind you not to forget to extend it to the parent node when extending outward, Because I once again

#pragma comment(linker, "/STACK:102400000,102400000")#include<iostream>#include<vector>#include<algorithm>#include<cstdio>#include<queue>#include<stack>#include<string>#include<map>#include<set>#include<cmath>#include<cassert>#include<cstring>#include<iomanip>using namespace std;#ifdef _WIN32#define i64 __int64#define out64 "%I64d\n"#define in64 "%I64d"#else#define i64 long long#define out64 "%lld\n"#define in64 "%lld"#endif/************ for topcoder by zz1215 *******************/#define foreach(c,itr)  for(__typeof((c).begin()) itr=(c).begin();itr!=(c).end();itr++)#define FOR(i,a,b)      for( int i = (a) ; i <= (b) ; i ++)#define FF(i,a)         for( int i = 0 ; i < (a) ; i ++)#define FFD(i,a,b)      for( int i = (a) ; i >= (b) ; i --)#define S64(a)          scanf(in64,&a)#define SS(a)           scanf("%d",&a)#define LL(a)           ((a)<<1)#define RR(a)           (((a)<<1)+1)#define pb              push_back#define pf              push_front#define X               first#define Y               second#define CL(Q)           while(!Q.empty())Q.pop()#define MM(name,what)   memset(name,what,sizeof(name))#define MC(a,b)memcpy(a,b,sizeof(b))#define MAX(a,b)        ((a)>(b)?(a):(b))#define MIN(a,b)        ((a)<(b)?(a):(b))#define read            freopen("out.txt","r",stdin)#define write           freopen("out2.txt","w",stdout)const int inf = 0x3f3f3f3f;const i64 inf64 = 0x3f3f3f3f3f3f3f3fLL;const double oo = 10e9;const double eps = 10e-9;const double pi = acos(-1.0);const int maxn = 211111;struct Node{int now;int to;int h;bool operator < (const Node & cmp) const{return h>cmp.h;}}node;int n;vector<Node>g[maxn];int dfv[maxn];int dfn[maxn];int t[maxn];int h[maxn];int df;vector<int>s;vector<int>si;bool vis[maxn];vector<int>line;int a[maxn];int ax[maxn][20];int dx[maxn][20];int lg2[maxn];bool isline[maxn];void dfs(){for (int i = 1; i <= n; i++){vis[i] = false;}df = 1;s.clear();si.clear();s.push_back(1);si.push_back(0);vis[1] = true;int now, to, id;while (!s.empty()){now = s.back();id = si.back();if (id < g[now].size()){to = g[now][id].to;si.back()++;if (!vis[to]){vis[to] = true;t[to] = now;s.push_back(to);si.push_back(0);}}else{dfv[df] = s.back();dfn[s.back()] = df++;s.pop_back();si.pop_back();}}}int find_len(int now){if (g[now].size() >= 2){return g[now][0].h + g[now][1].h;}else if (g[now].size() == 1){return g[now][0].h;}else{return 0;}}void get_line(int now){if (g[now].size() >= 2){int t1 = g[now][0].to;int t2 = g[now][1].to;isline[now] = true;while (true){isline[t1] = true;line.push_back(t1);if (g[t1].size() > 0){t1 = g[t1][0].to;}else{break;}}reverse(line.begin(), line.end());line.push_back(now);while (true){isline[t2] = true;line.push_back(t2);if (g[t2].size() > 0){t2 = g[t2][0].to;}else{break;}}}else if(g[now].size() ==1){while (true){isline[now] = true;line.push_back(now);if (g[now].size() > 0){now = g[now][0].to;}else{break;}}}}int max_way(int now){int to;int re = 0;for (int i = 0; i < g[now].size(); i++){to = g[now][i].to;if (!isline[to]){re = max(re, g[now][i].h);}}return re;}void sparse_table(){for (int i = 0; i < line.size(); i++){ax[i][0] = a[i]+i;dx[i][0] = a[i]+(int)line.size()-1-i;}for (int step = 1; (1 << step) < line.size(); step++){for (int i = 0; i < line.size(); i++){ax[i][step] = ax[i][step - 1];dx[i][step] = dx[i][step - 1];if (i + (1 << (step - 1)) < line.size()){ax[i][step] = max(ax[i][step], ax[i + (1 << (step - 1))][step - 1]);dx[i][step] = max(dx[i][step], dx[i + (1 << (step - 1))][step - 1]);}}}}int max_a(int l, int r){return max(ax[l][lg2[r - l + 1]], ax[r - (1 << lg2[r - l + 1]) + 1][lg2[r - l + 1]]);}int max_d(int l, int r){return max(dx[l][lg2[r - l + 1]], dx[r - (1 << lg2[r - l + 1]) + 1][lg2[r - l + 1]]);}int find(int l, int r){int mid = (r + l) / 2;return max(max_a(l, mid) - l, max_d(mid+1,r)-( (int)line.size()-1-r ) );}int back[maxn];void find_back(){for (int i = 1; i <= n; i++){back[i] = 0;}queue<int>q;q.push(1);int now, to,fa,temp;while (!q.empty()){now = q.front();q.pop();if (t[now]){fa = t[now];back[now] = 1 + back[fa];temp = 0;if (g[fa][0].to == now){if (g[fa].size() >= 2){temp = g[fa][1].h+1;}}else{temp = g[fa][0].h;}back[now] = max(back[now], temp);}for (int i = 0; i < g[now].size(); i++){q.push(g[now][i].to);}}}void start(){dfs();for (int i = 1; i <= n; i++){h[i] = 0;}vector<Node>gg;int now, to;for (now = 1; now <= n; now++){gg.clear();for (int i = 0; i < g[now].size(); i++){to = g[now][i].to;if (to != t[now]){gg.push_back(g[now][i]);}}g[now] = gg;}for (int x = 1; x < df; x++){now = dfv[x];for (int i = 0; i < g[now].size(); i++){to = g[now][i].to;h[now] = max(h[now], h[to] + 1);}}for (now = 1; now <= n; now++){for (int i = 0; i < g[now].size(); i++){to = g[now][i].to;g[now][i].h = h[to] + 1;}}for (now = 1; now <= n; now++){sort(g[now].begin(), g[now].end());}int id;int len = -1;int temp;for (now = 1; now <= n; now++){temp = find_len(now);if (temp > len){len = temp;id = now;}}for (int i = 1; i <= n; i++){isline[i] = false;}line.clear();get_line(id);find_back();for (int i = 0; i < line.size(); i++){a[i] = max_way(line[i]);if (line[i] == id){a[i] = max(a[i], back[id]);}}sparse_table();int ans=inf;int left;int right;int l, r;for (int lend = 0; lend < line.size(); lend++){l = lend;r = line.size() - 1;while (l + 2 < r){int mid = (l + r) / 2;if (find(lend, mid) > (int)line.size() - 1 - mid){r = mid;}else{l = mid;}}for (int x = l; x <= r; x++){temp = max(find(lend, x), (int)line.size() - 1 - x);temp = max(temp, lend);if (temp < ans){ans = temp;left = lend;right = x;}}}cout << ans << " " << line[left] << " " << line[right] << endl;}int main(){for (int i = 0; i < 20; i++){if ((1 << i) < maxn){lg2[1 << i] = i;}}for (int i = 3; i < maxn; i++){if (!lg2[i]){lg2[i] = lg2[i - 1];}}int T;cin >> T;while (T--){cin >> n;for (int i = 1; i <= n; i++){g[i].clear();}node.h = 0;for (int i = 1; i <= n - 1; i++){//cin >> node.now >> node.to;SS(node.now); SS(node.to);g[node.now].push_back(node);swap(node.now, node.to);g[node.now].push_back(node);}start();}return 0;}

Zoj 3820 4acm/ICPC Mudanjiang Division B