POJ 2114 Boatherds 树的分治

来源：互联网发布：那个漫画软件好最全编辑：程序博客网时间：2024/05/29 15:05

题目大意：给出一棵树，问有没有两点之间的距离是k的。多组数据

思路：和IOI2011的Race一样，比那个简单。读入太恶心了，我是上网上抄的别人的主函数。

CODE：

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#define MAX 10010#define INF 0x3f3f3f3fusing namespace std;int points,k;int head[MAX],total;int next[MAX << 1],aim[MAX << 1],length[MAX << 1]; int _total,_size,size[MAX];int ans,root;bool v[MAX];int dis[MAX],p;inline void Initialize();inline void Add(int x,int y,int len);void Work(int x);void GetRoot(int x,int last);inline int Count(int x,int last,int len);void GetDis(int x,int last,int len);int main(){while(scanf("%d",&points) != EOF && points) {Initialize();for(int y,z,i = 1;i <= points; ++i) {while(scanf("%d",&y) != EOF && y) {scanf("%d",&z);Add(i,y,z),Add(y,i,z);}}while(scanf("%d",&k) != EOF && k) {ans = 0;size[1] = points;memset(v,false,sizeof(v));Work(1);if(ans)puts("AYE");elseputs("NAY");}puts(".");}return 0;}inline void Initialize(){total = 0;memset(head,0,sizeof(head));}inline void Add(int x,int y,int len){next[++total] = head[x];aim[total] = y;length[total] = len;head[x] = total;}void Work(int x){_size = INF,_total = size[x];GetRoot(x,0);x = root;v[x] = true;ans += Count(x,0,0);for(int i = head[x];i;i = next[i]) {if(v[aim[i]])continue;ans -= Count(aim[i],x,length[i]);Work(aim[i]);}}void GetRoot(int x,int last){size[x] = 1;int max_size = 0;for(int i = head[x];i;i = next[i]) {if(aim[i] == last || v[aim[i]])continue;GetRoot(aim[i],x);size[x] += size[aim[i]];max_size = max(max_size,size[aim[i]]); }max_size = max(max_size,_total - size[x]);if(max_size < _size)_size = max_size,root = x;}inline int Count(int x,int last,int len){p = 0;GetDis(x,last,len);sort(dis + 1,dis + p + 1);int l = 1,r = p,re = 0;while(l < r) {if(dis[l] + dis[r] > k)--r;else if(dis[l] + dis[r] < k)++l;else {if(dis[r] == dis[l]) {re += (r - l) * (r - l + 1) >> 1;break;}int _l = l,_r = r;while(dis[l] == dis[_l])_l++;while(dis[r] == dis[_r])_r--;re += (_l - l) * (r - _r);l = _l,r = _r;}} return re;}void GetDis(int x,int last,int len){dis[++p] = len;for(int i = head[x];i;i = next[i]) {if(aim[i] == last || v[aim[i]])continue;GetDis(aim[i],x,len + length[i]);}}

0 0