CF1272 E.Nearest Opposite Parity（反向建图+BFS）

///#pragma GCC optimize(3)
///#pragma GCC optimize("Ofast","unroll-loops","omit-frame-pointer","inline")
///#pragma GCC optimize(2)
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll>PLL;
typedef pair<int,int>PII;
typedef pair<double,double>PDD;
#define I_int ll
inline ll read()
{
    ll x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
char F[200];
inline void out(I_int x) {
    if (x == 0) return (void) (putchar('0'));
    I_int tmp = x > 0 ? x : -x;
    if (x < 0) putchar('-');
    int cnt = 0;
    while (tmp > 0) {
        F[cnt++] = tmp % 10 + '0';
        tmp /= 10;
    }
    while (cnt > 0) putchar(F[--cnt]);
    //cout<<" ";
}
ll ksm(ll a,ll b,ll p){ll res=1;while(b){if(b&1)res=res*a%p;a=a*a%p;b>>=1;}return res;}
const ll inf = 0x3f3f3f3f3f3f3f3f;
const int maxn=1e6+100,N=1e6+100;
const double PI = atan(1.0)*4;
const double eps=1e-6;
int h[maxn],idx;
struct node{
    int e,ne;
}edge[maxn*2];
void add(int u,int v){
    edge[idx].e=v,edge[idx].ne=h[u],h[u]=idx++;
}
int a[maxn];
int n;
int res[maxn],dp[maxn];
int vis[maxn];
void bfs1(){///奇数变为偶数
    queue<int>q;
    for(int i=1;i<=n;i++){
        if(a[i]%2) q.push(i),dp[i]=0,vis[i]=0;
        else vis[i]=-1,dp[i]=-1;
    }
    while(!q.empty()){
        int t=q.front();q.pop();
        for(int i=h[t];~i;i=edge[i].ne){
            int j=edge[i].e;
            if(vis[j]==-1){
                q.push(j);
                vis[j]=1;
                dp[j]=dp[t]+1;
            }
        }
    }
}
int dp1[maxn];
int vis1[maxn];
void bfs2(){///偶数能否bfs到奇数
    queue<int>q;
    for(int i=1;i<=n;i++){
        if(a[i]%2==0) q.push(i),dp1[i]=0,vis1[i]=0;
        else vis1[i]=-1,dp1[i]=-1;
    }
    while(!q.empty()){
        int t=q.front();q.pop();
        for(int i=h[t];~i;i=edge[i].ne){
            int j=edge[i].e;
            if(vis1[j]==-1){
                dp1[j]=dp1[t]+1;
                vis1[j]=1;
                q.push(j);
            }
        }
    }
}
int main(){
    memset(res,0x3f,sizeof res);
    memset(h,-1,sizeof h);
    n=read();
    for(int i=1;i<=n;i++){
        a[i]=read();
        int tmp=i+a[i];
        if(tmp<=n&&tmp>=1) add(tmp,i);
        tmp=i-a[i];
        if(tmp<=n&&tmp>=1) add(tmp,i);
    }
    bfs1();bfs2();
    for(int i=1;i<=n;i++)
        if(a[i]%2) cout<<dp1[i]<<" ";
        else cout<<dp[i]<<" ";
    return 0;
}