Concept of Tree

Storage and Traversal of Trees

和图的存储一致（建议用邻接表存储和链式前向星存储）

DFS遍历

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#include <bits/stdc++.h>
using namespace std;

const int N = 1e5+5;

struct node
{ 
    int nxt, to, cost;
    node(){}
    node(int x, int v, int c){ nxt = x, to = v, cost = c; }
}e[N<<1];

int Cnt = 0, head[N];
void Add_Edge(int u, int v, int c)
{
    e[Cnt] = node(head[u], v, c);
    head[u] = Cnt++;
}

int n, u, v, c, root, fa[N], dep[N], dis[N];
void dfs(int u, int f)
{
	dep[u] = dep[f] + 1;
	fa[u] = f;
	for(int i = head[u]; ~i; i = e[i].nxt)
	{
		int v = e[i].to, c = e[i].cost;
		if(v == f)continue;
		dis[v] = dis[u] + c;
		dfs(v, u);
	}
}

int main()
{
	cin>>n;
	root = 1;
	memset(head, -1, sizeof(head));
	for(int i = 1; i<n; ++i)
	{
		cin>>u>>v>>c;
		Add_Edge(u, v, c);
		Add_Edge(v, u, c);
	}
	dfs(root, 0);
	for(int i = 1; i<=n; ++i)
	{
		printf("%d : deep = %d, distance = %d, father = %d\n", i, dep[i], dis[i], fa[i]);
	}
}

左右儿子记录法（二叉树）

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#include <bits/stdc++.h>
using namespace std;

const int N = 1e5+5;

int root, n;

struct Node
{
	int ls, rs;
	Node(){ ls = 0, rs = 0;	}
	Node(int l, int r){ ls = l, rs = r;	}
}a[N];

//二叉树遍历
void pre(int x)    //先序遍历(根左右)
{
	if(!x) return;
	printf("%d ", x);
	pre(a[x].ls);
	pre(a[x].rs);
}
void mid(int x)  //中序遍历(左根右)
{
	if(!x) return;
	mid(a[x].ls);
	printf("%d ", x);
	mid(a[x].rs);
}
void last(int x)  //后序遍历(左右根)
{
	if(!x) return;
	last(a[x].ls);
	last(a[x].rs);
	printf("%d ", x);
}
int main()
{
	cin>>n>>root;
	for(int i = 1; i<=n; ++i)   //左右儿子记录法
	{
		cin>>ls>>rs;
		a[i] = Node(ls, rs);
	}
}

Thanks to SZUACM