Codeforces 761E Dasha and Puzzle【构造,树dfs】
2017-02-28 18:24
423 查看
题目:http://codeforces.com/contest/761/problem/E
题意:
给出n(n<=30)个节点的树,给每个点确定一个坐标,使得n-1跳边和坐标轴平行。要保证所有的边都不想交。分析:
很显然,如果某个点的度大于4,那么无解。那么问题的就变成了从一个点出发,把所有邻接点向上下左右四个方向确定即可。
问题的关键是怎么使得所有的边不会相交?
提示:20 + 21 + ... + 2k < 2k + 1.
代码:
#include <bits/stdc++.h> using namespace std; #define pb push_back #define mp make_pair #define fr first #define sc second #define sz(v) ((int)(v).size()) typedef long long lld; typedef pair<int, int> pii; int dx[] = {0, 1, 0, -1},dy[] = {-1, 0, 1, 0}; lld x[MAXN], y[MAXN]; vector <int> con[MAXN]; bool dfs(int n,int d,int from,int step) { if(con .size()>4)return 0; vector<int>a,b; for(int i=0; i<con .size(); i++)if(con [i]!=from)a.pb(con [i]); for(int i=0; i<4; i++)if(i!=d)b.pb(i); lld dis=1LL<<step; for(int i=0; i<a.size(); i++) { int t=a[i],d=b[i]; x[t]=x +dis*dx[d]; y[t]=y +dis*dy[d]; if(!dfs(t,(d+2)%4,n,step-1))return 0; } return 1; } int main() { // freopen("in.txt","r",stdin); int n; scanf("%d", &n); for (int i=1; i<n; i++) { int a, b; scanf("%d%d", &a, &b); con[a].pb(b); con[b].pb(a); } if (!dfs(1, -1, 0, 50)) { puts("NO"); return 0; } puts("YES"); for (int i=1; i<=n; i++) printf("%lld %lld\n", x[i], y[i]); }
相关文章推荐
- codeforces 840B. Leha and another game about graph(构造,dfs)
- codeforces 359E Neatness(DFS+构造)
- CodeForces - 841D Leha and another game about graph 构造(dfs + 思维)
- Codeforces 906B. Seating of Students(构造+DFS)
- 【打CF,学算法——二星级】CodeForces 96B Lucky Numbers (构造/dfs)
- Codeforces 731C Socks【Dfs+贪心】
- codeforces 653B B. Bear and Compressing(dfs)
- CodeForces 417E (构造)
- codeforces 891B Gluttony (构造+思维)
- codeforces 258B Little Elephant and Elections 数位DP+DFS
- 【codeforces 725C】C. Hidden Word【字符串构造】
- codeforces 550B Preparing Olympiad(DFS+回溯)
- CodeForces 303 A.Lucky Permutation Triple(构造)
- Codeforces 842 C. Ilya And The Tree (dfs)
- 【dfs+理解题意+构造】【待重做】codeforces E. Ice cream coloring
- Codeforces 659E New Reform【DFS】
- Codeforces 700B Connecting Universities(DFS)
- Codeforces 364 A Matrix 题解(矩形构造)
- codeforces_622D. Optimal Number Permutation(构造)
- Codeforces-148C-standard output(构造)