G. Lights

合集 - codeforces(57)

1.C. Insert and Equalize2023-12-062.C. Removal of Unattractive Pairs2023-12-063.D. Jumping Through Segments2023-12-084.E. Good Triples2023-12-085.F. Shift and Reverse2023-12-086.D. Yet Another Monster Fight2023-12-117.A. Constructive Problems2023-12-188.C. Game with Multiset2023-12-199.A. Rating Increase2023-12-1910.B. Swap and Delete2023-12-1911.A. Problemsolving Log2023-12-2012.B. Preparing for the Contest2023-12-2013.C. Quests2023-12-2014.D. Three Activities2023-12-2015.E2. Game with Marbles (Hard Version)2023-12-2016.cf刷题有感2023-12-2017.A. Anonymous Informant2023-12-2118.A. Forked!2023-12-2319.B. Make Almost Equal With Mod2023-12-2720.C. Heavy Intervals2023-12-2721.D. Split Plus K2023-12-2822.A. 20232023-12-3123.B. Two Divisors2023-12-3124.C. Training Before the Olympiad2023-12-3125.D. Mathematical Problem2024-01-0226.F. Greetings2024-01-0227.C. Partitioning the Array2024-01-1528.G. Bicycles2024-01-1629.E. Eat the Chip2024-01-17

30.G. Lights2024-01-17

31.D. Array Repetition2024-01-1732.D. Berserk Monsters2024-01-2233.E. Increasing Subsequences2024-01-2334.D. Very Different Array2024-01-2435.G. Mischievous Shooter2024-01-2536.B. Plus-Minus Split2024-01-2737.B. A Balanced Problemset2024-01-2838.C. Did We Get Everything Covered2024-01-2839.D. Find the Different Ones!2024-02-0840.C. Grouping Increases2024-02-1041.D. Good Trip2024-02-1242.C. Physical Education Lesson2024-02-1243.E. Final Countdown2024-02-1844.D. Divisible Pairs2024-02-1945.G. Vlad and Trouble at MIT2024-02-2046.A. Brick Wall2024-02-2847.B. Minimize Inversions2024-02-2848.C. XOR-distance2024-02-2849.A. Moving Chips2024-02-2850.B. Monsters Attack!2024-02-2851.C. Find B2024-02-2852.D. Slimes2024-02-2853.C. Turtle Fingers: Count the Values of k2024-02-2854.D. Turtle Tenacity: Continual Mods2024-02-2855.D. Vlad and Division2024-02-2856.C. LR-remainders2024-02-2857.D. Lonely Mountain Dungeons2024-03-12

收起

原题链接

太巧妙了！！

关键1：把开着的灯当成黑点看待
关键二：如图

更多细节请看代码

code

#include<bits/stdc++.h>
using namespace std;
int to[100005];//代表会被我影响的灯，抽象成边
void solve()
{
        int n;
        int state[100005]={0};//代表每个灯的状态
        int ind[100005]={0};//代表入度
        string s;
        cin>>n>>s;
        vector<int> ans;//代表答案，需要关掉灯的编号
        for(int i=1;i<=n;i++)
        {
            cin>>to[i];
            ind[to[i]]++;
            if(s[i-1]=='1')state[i]=1;//用数组代替，方便计算
        }

        queue<int> q;
        for(int i=1;i<=n;i++) if(!ind[i]) q.push(i);//从入度为零的点开始消除，即消除链

        while(q.size())
        {
            int now=q.front();
            q.pop();
            if(--ind[to[now]]==0)q.push(to[now]);
            if(state[now])//把开着的灯想象成黑色的点，开关后，黑点会向下移动，且黑点遇到黑点时会消除
            {
                ans.push_back(now);
                state[to[now]]^=1;
                state[now]=0;
            }
        }

        for(int i=1;i<=n;i++)
        {
            if(ind[i])//现在把链全部去掉了，环可能有多个
            {
                int x=i,len=0,half=0,curstate=0;
                while(ind[x]--)
                {
                    curstate^=state[x];
                    half+=curstate;
                    len++;
                    x=to[x];
                }
                if(curstate)
                {
                    cout<<"-1"<<endl;//如果环上的黑点奇数个，肯定无法消除
                    return;
                }

                for(int i=1;i<=len;i++)//这一段判断环上需要关掉灯的方法太巧妙了！！
                {
                    curstate^=state[x];
                    if(curstate==(2*half<=len))ans.push_back(x);
                    x=to[x];
                }
            }
        }

        cout<<ans.size()<<endl;
        for(int i:ans)cout<<i<<" ";
        cout<<endl;
}
int main()
{
    ios::sync_with_stdio(false);
    int t;
    cin>>t;
    while(t--) solve();
    return 0;
}