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  • Codeforces Round #451 (Div. 2) B. Proper Nutrition【枚举/扩展欧几里得/给你n问有没有两个非负整数x,y满足x·a + y·b = n】

    B. Proper Nutrition
    time limit per test
    1 second
    memory limit per test
    256 megabytes
    input
    standard input
    output
    standard output

    Vasya has n burles. One bottle of Ber-Cola costs a burles and one Bars bar costs b burles. He can buy any non-negative integer number of bottles of Ber-Cola and any non-negative integer number of Bars bars.

    Find out if it's possible to buy some amount of bottles of Ber-Cola and Bars bars and spend exactly n burles.

    In other words, you should find two non-negative integers x and y such that Vasya can buy x bottles of Ber-Cola and y Bars bars andx·a + y·b = n or tell that it's impossible.

    Input

    First line contains single integer n (1 ≤ n ≤ 10 000 000) — amount of money, that Vasya has.

    Second line contains single integer a (1 ≤ a ≤ 10 000 000) — cost of one bottle of Ber-Cola.

    Third line contains single integer b (1 ≤ b ≤ 10 000 000) — cost of one Bars bar.

    Output

    If Vasya can't buy Bars and Ber-Cola in such a way to spend exactly n burles print «NO» (without quotes).

    Otherwise in first line print «YES» (without quotes). In second line print two non-negative integers x and y — number of bottles of Ber-Cola and number of Bars bars Vasya should buy in order to spend exactly n burles, i.e. x·a + y·b = n. If there are multiple answers print any of them.

    Any of numbers x and y can be equal 0.

    Examples
    input
    7
    2
    3
    output
    YES
    2 1
    input
    100
    25
    10
    output
    YES
    0 10
    input
    15
    4
    8
    output
    NO
    input
    9960594
    2551
    2557
    output
    YES
    1951 1949
    Note

    In first example Vasya can buy two bottles of Ber-Cola and one Bars bar. He will spend exactly 2·2 + 1·3 = 7 burles.

    In second example Vasya can spend exactly n burles multiple ways:

    • buy two bottles of Ber-Cola and five Bars bars;
    • buy four bottles of Ber-Cola and don't buy Bars bars;
    • don't buy Ber-Cola and buy 10 Bars bars.

    In third example it's impossible to but Ber-Cola and Bars bars in order to spend exactly n burles.

    【题意】:给你n问有没有两个非负整数x,y满足x·a + y·b = n。

     【分析】:略带技巧的枚举。非负整数x,y上面做文章。

    【代码】:

    #include<bits/stdc++.h>
    using namespace std;
    int main()
    {
        int n,a,b;
        cin>>n>>a>>b;
        for(int i=0;i*a<=n;++i)//自己这个地方是i<=n,错了,可能出现到负数的时候%b==0的情况
        {
            if((n-i*a)%b==0)
            {
                int j=(n-i*a)/b;
                puts("YES");
                printf("%d %d
    ",i,j);
                exit(0);
            }
        }
        puts("NO");
        return 0;
    }
    枚举,整数性判断
    #include <bits/stdc++.h>
    
    using namespace std;
    typedef long long int ll;
    ll ex_gcd(ll a,ll b,ll &x,ll &y)
    {
        if(b==0)
        {
            x=1;
            y=0;
            return a;
        }
       ll r=ex_gcd(b,a%b,x,y);
        ll t=x;
        x=y;
        y=t-a/b*y;
        return r;
    }
    bool jie(ll a,ll b,ll c,ll &x,ll &y)
    {
        ll r=ex_gcd(a,b,x,y);
        if(c%r!=0) return 0;
        ll zz=c/r;
        x*=zz;
        y*=zz;
        if(x<0&&y<0) return 0;
         ll bb=b/r;
         ll aa=a/r;
        if(x<0&&y>0)
        {
            ll t=-1*x/bb;
            if(x+bb*t<0) t++;
            x=x+bb*t;
            y=y-aa*t;
            if(y>=0) return 1;
            else return 0;
        }
       else if(x>0&&y<0)
        {
            ll t=y/aa;
            if(y-aa*t<0) t--;
    
            x=x+bb*t;
            y=y-aa*t;
            if(x>=0) return 1;
            else return 0;
        }
        return 1;
    }
    ll a,b,n,x,y;
    int main()
    {
        while(~scanf("%lld%lld%lld",&n,&a,&b))
        {
            x=0;
            y=0;
            if(jie(a,b,n,x,y))
            {
                printf("YES
    ");
                printf("%lld %lld
    ",x,y);
            }
            else
            {
                printf("NO
    ");
            }
        }
        return 0;
    }
    拓展欧几里得
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  • 原文地址:https://www.cnblogs.com/Roni-i/p/8087450.html
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