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  • codeforces#297div2_b 贪心,字符串,哈希

    codeforces#297div2_b 贪心,字符串

    Pasha got a very beautiful string s for his birthday, the string consists of lowercase Latin letters. The letters in the string are numbered from 1 to |s|from left to right, where |s| is the length of the given string.

    Pasha didn't like his present very much so he decided to change it. After his birthday Pasha spent m days performing the following transformations on his string — each day he chose integer ai and reversed a piece of string (a segment) from position ai to position |s| - ai + 1. It is guaranteed that ai ≤ |s|.

    You face the following task: determine what Pasha's string will look like after m days.

    Input

    The first line of the input contains Pasha's string s of length from 2 to 2·105 characters, consisting of lowercase Latin letters.

    The second line contains a single integer m (1 ≤ m ≤ 105) —  the number of days when Pasha changed his string.

    The third line contains m space-separated elements ai (1 ≤ aiai ≤ |s|) — the position from which Pasha started transforming the string on thei-th day.

    Output

    In the first line of the output print what Pasha's string s will look like after m days.

    Sample test(s)
    input
    abcdef
    1
    2
    output
    aedcbf
    input
    vwxyz
    2
    2 2
    output
    vwxyz
    input
    abcdef
    3
    1 2 3
    output
    fbdcea
    题意:如题
    思路:由于对每个字符,翻转两次等于没翻,因此统计每个字符的翻转次数,判断奇偶,一个一个翻,复杂度o(n+m)
    #include<iostream>
    #include<cstdio>
    #include<cstdlib>
    #include<cstring>
    #include<algorithm>
    #include<string>
    
    using namespace std;
    
    const int maxn=1000100;
    const int INF=(1<<29);
    const double EPS=0.0000001;
    
    string s;
    int m,a;
    int x[maxn];
    
    int main()
    {
        cin>>s>>m;
        memset(x,0,sizeof(x));
        while(m--){
            scanf("%d",&a);
            x[a]++;
            x[s.length()+1-a]++;
        }
        for(int i=1;i<=s.length()/2;i++) x[i]+=x[i-1];
        for(int i=1;i<=s.length()/2;i++){
            if(x[i]&1) swap(s[i-1],s[s.length()-i]);
        }
        cout<<s<<endl;
        return 0;
    }
    View Code
    没有AC不了的题,只有不努力的ACMER!
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  • 原文地址:https://www.cnblogs.com/--560/p/4417259.html
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