Codeforces Round #363 (Div. 2)D. Fix a Tree
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D. Fix a Tree
http://codeforces.com/problemset/problem/698/B
先判有无环,有环就在并集时标记,再判有无自反,有反就把所有自反和标记的数连上一个自反(改变自反+标记-1),没有就把一个标记的环变为自反,在把所有标记的连上它。(改变标记个)。
#include<algorithm>#include <iostream>#include <cstring>#include <cstdio>#include <vector>#include <queue>#include <map>#include <set>using namespace std;#define INT 2147483647#define Max 210000int n;int arr[Max];int pre[Max];int ans[Max];int Find(int a){ if(a==pre[a]) { return a; } return pre[a]=Find(pre[a]);}void init(){ for(int i=1; i<=n; i++) { pre[i]=i; }}int Union(int x,int y){ x=Find(x); y=Find(y); if(x!=y) { pre[x]=y; }}int main(){ scanf("%d",&n); init(); int cnt=0; for(int i=1; i<=n; i++) { scanf("%d",&arr[i]); if(Find(arr[i])==Find(i)&&arr[i]!=i) { ans[++cnt]=i; } Union(i,arr[i]); } bool flag=false; int ant; for(int i=1; i<=n; i++) { if(arr[i]==i) { flag=true; ant=i; ans[++cnt]=i; } } printf("%d\n",cnt-(flag?1:0)); sort(ans+1,ans+cnt+1); int num=1; for(int i=1; i<=n; i++) { if(i!=1) { printf(" "); } if(num<=cnt&&i==ans[num]) { if(!flag) { printf("%d",ans[cnt]); } else { printf("%d",ant); } num++; } else { printf("%d",arr[i]); } } printf("\n"); return 0;}
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