【DFS——Codeforces Beta Round #14 (Div. 2)】D. Two Paths

#include <map>#include <set>#include <list>#include <queue>#include <deque>#include <stack>#include <string>#include <time.h>#include <cstdio>#include <math.h>#include <iomanip>#include <cstdlib>#include <limits.h>#include <string.h>#include <iostream>#include <fstream>#include <algorithm>using namespace std;#define LL long long#define MIN INT_MIN#define MAX INT_MAX#define PI acos(-1.0)#define FRE freopen ("input.txt","r",stdin)#define FF  freopen ("output.txt","w",stdout)#define N 205vector<int> v[N];int maxm;int dep;int dfs(int x,int pre) {    int res = 0;    int d1 = 0,d2 = 0;//最大&次大    int i,j;    for (i = 0; i < v[x].size(); i++) {        if (v[x][i] != pre) {            res = max(res,dfs(v[x][i],x));            if (dep > d1) {                d2 = d1;                d1 = dep;            } else {                d2 = max(dep,d2);            }        }    }    res = max(res,d1+d2);    dep = d1 + 1;    return res;}int main () {    int n;    scanf("%d",&n);    int i,j;    int t = n - 1;    while  (t--) {        int a,b;        scanf("%d%d",&a,&b);        v[a].push_back(b);        v[b].push_back(a);    }    maxm = 0;    //枚舉每條邊    for (i = 1; i <= n; i++) {        for (j = 0; j < v[i].size(); j++) {            int x = i;            int y = v[i][j];            int a = dfs(x,y);            int b = dfs(y,x);            if(a*b > maxm) {                maxm = a*b;            }        }    }    printf("%d\n",maxm);    return 0;}