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Educational Codeforces Round 19 D. Broken BST

思考的鸿毛 2022-04-27 阅读 25
c++
#include<bits/stdc++.h>
using namespace std;
const int N=2e5+10;
int n,val[N],l,r,res=0;
vector<int> v[N];
map<int,int> vis;
set<int> s;
void dfs(int p,int l,int r){
    if(l>r) return ;
    // cout<<"rt: "<<p<<" "<<val[p]<<" "<<l<<" "<<r<<endl;
    if(val[p]>l&&val[p]<r) s.insert(val[p]);
    if(v[p][0]!=-1) dfs(v[p][0],l,min(r,val[p]));
    if(v[p][1]!=-1) dfs(v[p][1],max(l,val[p]),r);
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%d%d%d",&val[i],&l,&r);
        v[i].push_back(l);
        v[i].push_back(r);
        vis[l]=vis[r]=1;
    }
    int rt=0;
    for(int i=1;i<=n;i++) if(vis.count(i)==0) rt=i;
    dfs(rt,-1,1e9+1); 
    for(int i=1;i<=n;i++) if(s.count(val[i])==0) ++res;
    cout<<res<<endl;
}
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