• Codeforces Round #319 (Div. 2) B. Modulo Sum 抽屉原理+01背包


    B. Modulo Sum
    time limit per test
    2 seconds
    memory limit per test
    256 megabytes
    input
    standard input
    output
    standard output

    You are given a sequence of numbers a1, a2, ..., an, and a number m.

    Check if it is possible to choose a non-empty subsequence aij such that the sum of numbers in this subsequence is divisible by m.

    Input

    The first line contains two numbers, n and m (1 ≤ n ≤ 106, 2 ≤ m ≤ 103) — the size of the original sequence and the number such that sum should be divisible by it.

    The second line contains n integers a1, a2, ..., an (0 ≤ ai ≤ 109).

    Output

    In the single line print either "YES" (without the quotes) if there exists the sought subsequence, or "NO" (without the quotes), if such subsequence doesn't exist.

    Examples
    input
    3 5
    1 2 3
    output
    YES
    input
    1 6
    5
    output
    NO
    input
    4 6
    3 1 1 3
    output
    YES
    input
    6 6
    5 5 5 5 5 5
    output
    YES
    题意:从n个数中选取任意个数(最少一个)使得对m取模为0;
    思路:首先当n>m的时候,是必定的;
        根据抽屉原理,前缀和必定有两个相等的数;sl==sr;
        sr-sl=0;意思就是[l,r]的和%m==0;
      n<m时,利用01背包,复杂度n*m;
    #include<bits/stdc++.h>
    using namespace std;
    #define ll __int64
    #define mod 1000000007
    #define pi (4*atan(1.0))
    const int N=1e3+10,M=1e6+10,inf=1e9+10;
    int a[M];
    int dp[N][N];
    int max(int x,int y,int z)
    {
        return max(x,max(y,z));
    }
    int main()
    {
        int x,y,z,i,t;
        memset(dp,0,sizeof(dp));
        scanf("%d%d",&x,&y);
        for(i=0;i<x;i++)
        scanf("%d",&a[i]);
        if(x>y)
        {
            printf("YES
    ");
            return 0;
        }
        for(i=0;i<x;i++)
        dp[i][(a[i]%y)]=1;
        for(i=1;i<x;i++)
        {
            for(t=0;t<y;t++)
            {
                dp[i][t]=max(dp[i][t],dp[i-1][t]);
                dp[i][(t+a[i])%y]=max(dp[i-1][t],dp[i][(t+a[i])%y]);
            }
        }
        if(dp[x-1][0])
            printf("YES
    ");
        else
            printf("NO
    ");
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/jhz033/p/5573483.html
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