CCF-CSP题解 201503-4 网络延时

求树的直径。

两遍(dfs)就好了。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <stack>
const int maxn = 10000;
const int maxm = 10000;

using namespace std;

int to[(maxn + maxm) * 2 + 10];
int nex[(maxn + maxm) * 2 + 10];
int head[maxn + maxm + 10], cnt = 0;

void addEdge(int a, int b)
{
    to[cnt] = b; nex[cnt] = head[a]; head[a] = cnt++;
    to[cnt] = a; nex[cnt] = head[b]; head[b] = cnt++;
}

int ans, depth;

void dfs(int x, int f, int d)
{
    if (d > depth)
        ans = x, depth = d;
    for (int i = head[x]; i != -1; i = nex[i])
    {
        int l = to[i];
        if (l != f)
            dfs(l, x, d + 1);
    }
}

int main()
{
    int n, m;
    scanf("%d%d", &n, &m);

    memset(head, -1, sizeof(head));

    for (int i = 2, temp; i <= n; i++)
    {
        scanf("%d", &temp);
        addEdge(i, temp);
    }

    for (int i = 1, temp; i <= m; i++)
    {
        scanf("%d", &temp);
        addEdge(i + n, temp);
    }

    ans = depth = -1;
    dfs(1, 1, 0);

    depth = -1;
    dfs(ans, ans, 0);

    printf("%d
", depth);

    return 0;
}