1021 Deepest Root --dfs-优快云博客

本文链接：https://blog.youkuaiyun.com/lhfl911/article/details/53454370

本文介绍了一种使用深度优先搜索计算树直径的方法。首先确保输入构成单一连通组件（树），然后通过两次深度优先搜索找到树的两个极端节点，这两个节点间的最长路径即为树的直径。

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先判断是不是树，并查集和深搜都可以
求树的直径，两遍搜索，答案为其合集。

#include <cstdio>
#include <cstring>
#include <vector>
#include <set>
#include <algorithm>
using namespace std;

const int MAXN = 10010;

vector<int> mp[MAXN];
bool vis[MAXN];
int num = 0;
int len = 0;
int dep[MAXN];

void book(int x) {
    vis[x] = true;
    for (int i = 0; i < mp[x].size(); i++)
        if (!vis[mp[x][i]])
            book(mp[x][i]);
}

void dfs(int f, int x, int d) {
    dep[x] = d;
    for (int i = 0; i < mp[x].size(); i++)
        if (mp[x][i] != f)
            dfs(x, mp[x][i], d+1);
}

int main() {
    int n;
    scanf("%d", &n);
    for (int i = 1; i < n; i++) {
        int x, y;
        scanf("%d%d", &x, &y);
        mp[x].push_back(y);
        mp[y].push_back(x);
    }

    memset(vis, false, sizeof(vis));
    for (int i = 1; i <= n; i++) 
        if (!vis[i]) {
            num++;
            book(i);
        }

    if (num > 1) {
        printf("Error: %d components\n", num);
        return 0;
    }

    set<int> s;
    dfs(0, 1, 0);
    int tmp = 1, ma = 0;
    for (int i = 2; i <= n; i++)
        if (dep[i] > ma) {
            ma = dep[i];
            tmp = i;
        }
    for (int i = 1; i <= n; i++)
        if (dep[i] == ma)
            s.insert(i);

    dfs(0, tmp, 0);
    ma = 0;
    for (int i = 1; i <= n; i++)
        ma = max(ma, dep[i]);
    for (int i = 1; i <= n; i++)
        if (dep[i] == ma)
            s.insert(i);

    for (set<int>::iterator it = s.begin(); it != s.end(); it++)
        printf("%d\n", *it);

    return 0;
}