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  • cf500A New Year Transportation

    A. New Year Transportation
    time limit per test 2 seconds
    memory limit per test 256 megabytes
    input standard input
    output standard output

    New Year is coming in Line World! In this world, there are n cells numbered by integers from 1 to n, as a 1 × n board. People live in cells. However, it was hard to move between distinct cells, because of the difficulty of escaping the cell. People wanted to meet people who live in other cells.

    So, user tncks0121 has made a transportation system to move between these cells, to celebrate the New Year. First, he thought of n - 1 positive integers a1, a2, ..., an - 1. For every integer iwhere 1 ≤ i ≤ n - 1 the condition 1 ≤ ai ≤ n - i holds. Next, he made n - 1 portals, numbered by integers from 1 to n - 1. The i-th (1 ≤ i ≤ n - 1) portal connects cell i and cell (i + ai), and one can travel from cell i to cell (i + ai) using the i-th portal. Unfortunately, one cannot use the portal backwards, which means one cannot move from cell (i + ai) to cell i using the i-th portal. It is easy to see that because of condition 1 ≤ ai ≤ n - i one can't leave the Line World using portals.

    Currently, I am standing at cell 1, and I want to go to cell t. However, I don't know whether it is possible to go there. Please determine whether I can go to cell t by only using the construted transportation system.

    Input

    The first line contains two space-separated integers n (3 ≤ n ≤ 3 × 104) and t (2 ≤ t ≤ n) — the number of cells, and the index of the cell which I want to go to.

    The second line contains n - 1 space-separated integers a1, a2, ..., an - 1 (1 ≤ ai ≤ n - i). It is guaranteed, that using the given transportation system, one cannot leave the Line World.

    Output

    If I can go to cell t using the transportation system, print "YES". Otherwise, print "NO".

    Sample test(s)
    Input
    8 4
    1 2 1 2 1 2 1
    Output
    YES
    Input
    8 5
    1 2 1 2 1 1 1
    Output
    NO
    Note

    In the first sample, the visited cells are: 1, 2, 4; so we can successfully visit the cell 4.

    In the second sample, the possible cells to visit are: 1, 2, 4, 6, 7, 8; so we can't visit the cell 5, which we want to visit.

    其实是好sb的一道题

    因为每个点都只能往右走而且目标唯一,所以怎么搞都行啊

    我傻傻的写了爆搜

    #include<cstdio>
    #include<iostream>
    #include<cstring>
    #include<cstdlib>
    #include<algorithm>
    #include<cmath>
    #include<queue>
    #include<deque>
    #include<set>
    #include<map>
    #include<ctime>
    #define LL long long
    #define inf 0x7ffffff
    #define pa pair<int,int>
    #define pi 3.1415926535897932384626433832795028841971
    using namespace std;
    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;
    }
    bool mrk[100010];
    int a[100010];
    int n,m;
    inline void dfs(int x)
    {
    	mrk[x]=1;
    	if (!mrk[x+a[x]])dfs(x+a[x]);
    }
    int main()
    {
    	n=read();m=read();
    	for(int i=1;i<n;i++)a[i]=read();
    	dfs(1);
    	if (mrk[m])	printf("YES");
    	else printf("NO");
    }
    
    ——by zhber,转载请注明来源
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  • 原文地址:https://www.cnblogs.com/zhber/p/4196469.html
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