HDU 4496 D-city (query set)

Question: Give You N points and M sides, and ask how many connected parts are there before the I side is deleted.

Train of Thought: from the back-to-front operation, adding an I-I edge from the back-to-back is equal to adding M-I edge and then deleting the front m-I edge. We can see that there is no edge at the beginning, so sum [m] = N;

#include <stdio.h>  #include <iostream>  #include <algorithm>  #include <string.h>  #include <queue> #include <math.h>  #define M 100010#define LL long long  using namespace std;int n,m;int father[M];int find(int x)  {    if(x!=father[x])     return father[x]=find(father[x]);    return x;  }  int sum[M];int main(){    while(~scanf("%d%d",&n,&m))    {        int a[M],b[M];        for(int i=0;i<=n;i++)            father[i]=i;        for(int i=1;i<=m;i++)            scanf("%d%d",&a[i],&b[i]);        sum[m]=n;        for(int i=m;i>0;i--)        {            if(find(a[i])!=find(b[i]))            {                sum[i-1]=sum[i]-1;                father[find(a[i])]=find(b[i]);            }            else                 sum[i-1]=sum[i];        }        for(int i=1;i<=m;i++)        {            printf("%d\n",sum[i]);        }    }    return 0;}