D. Harmonious Graph

题目：D. Harmonious Graph

总结：将每一个连通块的所有点都指向该连通图的最大点。从1点开始遍历，假设fa[1] = x;那么从2~(x-1)的所有点的根结点都一定会指向x。(是在一个连通块),如果此时有一个点的根结点是y，不是x,那么就需要把这两个连通块连起来了。这时候从2开始到max(x,y),都一定是的根结点一定都是指向max(x,y),所以x的值要选择大的。避免两个连通块有重复的。此时就是和别的连通块做比较了。

#include <bits/stdc++.h>
using namespace std;
const int N = 2e5+10;int fa[N],n,m;int Find(int x){if(fa[x] == x) return x;fa[x] = Find(fa[x]);return fa[x];
}
int main(){scanf("%d%d",&n,&m);for(int i = 1;i <= n;i++) fa[i] = i;while(m--){int x,y,fx,fy;scanf("%d%d",&x,&y);fx = Find(x);fy = Find(y);//   printf("%d %d\n",fx,fy);if(fx > fy) swap(fx,fy);fa[fx] = fy;//大的做父亲结点}int ans = 0;for(int i = 1;i <= n;i++){int x = Find(i);while(i < x){int y  = Find(i);//  printf("%d %d %d\n",i,y,x);if(x != y){ans++;//为什么要把x变大呢，如果两个连通块通过一条线已经连起来。那么这两个连通块的根节点最大，否则会有重复的if(x < y) swap(x,y);fa[y] = x;}i++;}}printf("%d\n",ans);return 0;
}

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