POJ-3630-Phone List(字典树)

链接:

https://vjudge.net/problem/POJ-3630

题意:

Given a list of phone numbers, determine if it is consistent in the sense that no number is the prefix of another. Let's say the phone catalogue listed these numbers:

Emergency 911
Alice 97 625 999
Bob 91 12 54 26
In this case, it's not possible to call Bob, because the central would direct your call to the emergency line as soon as you had dialled the first three digits of Bob's phone number. So this list would not be consistent.

思路:

建立字典树, 检查每一个结束的点, 后面有没有点了, 如果有说明存在前缀.
否则就没有.

代码:

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;

LL R[50], M[50];
int n;

LL ExGcd(LL a, LL b, LL &x, LL &y)
{
    if (b == 0)
    {
        x = 1, y = 0;
        return a;
    }
    LL d = ExGcd(b, a%b, x, y);
    LL tmp = y;
    y = x-(a/b)*y;
    x = tmp;
    return d;
}

LL ExCRT()
{
    LL m = M[1], r = R[1], x, y, gcd;
    for (int i = 2;i <= n;i++)
    {
        gcd = ExGcd(m, M[i], x, y);
        if ((r-R[i])%gcd != 0)
            return -1;
        x = (r-R[i])/gcd*x%M[i];
        r -= m*x;
        m = m/gcd*M[i];
        r %= m;
    }
    return (r%m+m)%m;
}

int main()
{
    scanf("%d", &n);
    for (int i = 1;i <= n;i++)
        scanf("%lld%lld", &M[i], &R[i]);
    printf("%lld\n", ExCRT());

    return 0;
}