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  • Codeforces 782C. Andryusha and Colored Balloons 搜索

    C. Andryusha and Colored Balloons
    time limit per test:2 seconds
    memory limit per test:256 megabytes
    input:standard input
    output:standard output

    Andryusha goes through a park each day. The squares and paths between them look boring to Andryusha, so he decided to decorate them.

    The park consists of n squares connected with (n - 1) bidirectional paths in such a way that any square is reachable from any other using these paths. Andryusha decided to hang a colored balloon at each of the squares. The baloons' colors are described by positive integers, starting from 1. In order to make the park varicolored, Andryusha wants to choose the colors in a special way. More precisely, he wants to use such colors that if a, b and c are distinct squares that a and b have a direct path between them, and b and c have a direct path between them, then balloon colors on these three squares are distinct.

    Andryusha wants to use as little different colors as possible. Help him to choose the colors!

    Input

    The first line contains single integer n (3 ≤ n ≤ 2·105) — the number of squares in the park.

    Each of the next (n - 1) lines contains two integers x and y (1 ≤ x, y ≤ n) — the indices of two squares directly connected by a path.

    It is guaranteed that any square is reachable from any other using the paths.

    Output

    In the first line print single integer k — the minimum number of colors Andryusha has to use.

    In the second line print n integers, the i-th of them should be equal to the balloon color on the i-th square. Each of these numbers should be within range from 1 to k.

    Examples
    Input
    3
    2 3
    1 3
    Output
    3
    1 3 2
    Input
    5
    2 3
    5 3
    4 3
    1 3
    Output
    5
    1 3 2 5 4
    Input
    5
    2 1
    3 2
    4 3
    5 4
    Output
    3
    1 2 3 1 2
    Note

    In the first sample the park consists of three squares: 1 → 3 → 2. Thus, the balloon colors have to be distinct.

    Illustration for the first sample.

    In the second example there are following triples of consequently connected squares:

    • 1 → 3 → 2
    • 1 → 3 → 4
    • 1 → 3 → 5
    • 2 → 3 → 4
    • 2 → 3 → 5
    • 4 → 3 → 5
    We can see that each pair of squares is encountered in some triple, so all colors have to be distinct.
    Illustration for the second sample.

    In the third example there are following triples:

    • 1 → 2 → 3
    • 2 → 3 → 4
    • 3 → 4 → 5
    We can see that one or two colors is not enough, but there is an answer that uses three colors only.
    Illustration for the third sample.
     
    题意:有一棵n个节点的树,现给节点着色,要求任意相邻的3个节点的颜色不能一样。输出使用颜色种类最少的结果。
    思路:dfs搜索。
    #include<iostream>
    #include<cstdio>
    #include<cstring>
    #include<algorithm>
    #include<map>
    #include<vector>
    using namespace std;
    const int MAXN=2e5+100,INF=0x3f3f3f3f,MOD=1e9+7;
    int n,col[MAXN];
    map<int,vector<int> >G;
    int ans;
    dfs(int now,int sign,int fa,int flag)
    {
        //cout<<now<<" "<<sign<<" "<<fa<<" "<<flag<<endl;
        int tmp=0;
        for(int i=0; i<G[now].size(); i++)
        {
            int to=G[now][i];
            if(to==fa) continue;
            while(++tmp)
            {
                if(tmp!=sign&&tmp!=flag)
                {
                    col[to]=tmp;
                    if(tmp>ans) ans=tmp;
                    dfs(to,tmp,now,sign);
                    break;
                }
            }
        }
    }
    int main()
    {
        scanf("%d",&n);
        for(int i=1; i<n; i++)
        {
            int u,v;
            scanf("%d%d",&u,&v);
            G[u].push_back(v);
            G[v].push_back(u);
        }
        col[1]=1;
        ans=1;
        dfs(1,1,-1,-1);
        cout<<ans<<endl;
        for(int i=1; i<=n; i++) cout<<col[i]<<" ";
        cout<<endl;
        return 0;
    }
    搜索
    I am a slow walker,but I never walk backwards.
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  • 原文地址:https://www.cnblogs.com/GeekZRF/p/6511369.html
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