朴素暴力做法

#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> e[1005]; // 记录每个点连向了哪些点
int dis[1005];       // 记录每个点的深度
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n;
    for (int i = 1; i <= n - 1; i++)
    {
        int u, v;
        cin >> u >> v;
        e[u].push_back(v);
        e[v].push_back(u);
    }
    for (int i = 1; i <= n; i++)
        dis[i] = -1;
    dis[1] = 0;
    for (int now = 0; now <= n; now++)
    {
        // 把所有深度为 now 的往下做一层
        for (int i = 1; i <= n; i++)
        {
            if (dis[i] != now)
                continue;
            // 把 i 相连的深度为 -1 的点，深度都改成 now+1
            for (int j = 0; j < e[i].size(); j++)
            {
                if (dis[e[i][j]] == -1)
                    dis[e[i][j]] = now + 1;
            }
        }
    }
    for (int i = 1; i <= n; i++)
        cout << dis[i] << " ";
    return 0;
}

常规搜索做法

#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> e[1005];
int dis[1005];
// 当前子树根节点，当前子树根节点的父节点
void dfs(int u, int fa)
{
    // 枚举所有u能连到的点v
    for (int i = 0; i < e[u].size(); i++)
    {
        int v = e[u][i];
        if (v == fa)
            continue; // 忽略父节点方向
        dis[v] = dis[u] + 1;
        dfs(v, u);
    }
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n;
    for (int i = 1; i <= n - 1; i++)
    {
        int u, v;
        cin >> u >> v;
        e[u].push_back(v);
        e[v].push_back(u);
    }
    dis[1] = 0;
    dfs(1, 0);
    for (int i = 1; i <= n; i++)
        cout << dis[i] << " ";
    cout << "\n";
    return 0;
}