HDU3988 WA 求找Bug！（c++）

Question

HDU3988 WA 求找Bug！（c++）
以下是die码：

# pragma GCC optimize("Ofast,no-stack-protector")

# pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

# include <bits/stdc++.h>

typedef long long ll;

using namespace std;

const int maxn = 1e7;

int t;

ll k, n, sum, minx, tot, m, p[670000], cnt; //664579

bitset <10000005> vis;

int main () {

    ios::sync_with_stdio (0);

    cin.tie (0);

    cout.tie (0);

    for (int i = 2; i * i <= maxn; ++ i)
        if (! vis[i])
            for (int j = i * i; j <= maxn; j += i)
                vis[j] = 1;

    for (int i = 2; i <= maxn; ++ i)
        if (! vis[i])
            p[++ cnt] = i;
//    cerr << m << '\n';
    cin >> t;

    for (int ca = 1; ca <= t; ++ ca) {

        cin >> k >> n;

        cout << "Case " << ca << ": ";

        if (k == 1) {

            cout << "inf\n";

            continue ;

        }

        minx = 9223372036854775807ll;

        for (ll i = 1; i <= cnt && p[i] * p[i] <= k; ++ i)
            if (! (k % p[i])) {

                tot = sum = 0, m = n;

                while (! (k % p[i]))
                    k /= p[i], ++ tot;

                while (m)
                    m /= p[i], sum += m;

                minx = min (minx, sum / tot);

            }

        if (k ^ 1) {

            sum = 0;

            m = n;

            while (m)
                m /= k, sum += m;

            minx = min (minx, sum);

        }

        cout << minx << '\n';

    }

    return 0;

}

Answer 1

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在您提供的代码中，我发现了一个可能导致WA（Wrong Answer）的问题。在计算最小值时，当k是一个质数且不等于1时，代码没有正确处理。下面是修复后的代码：

#include <iostream>
#include <vector>
#include <algorithm>
#include <bitset>
using namespace std;

const int maxn = 1e7;

int t;
long long k, n, sum, minx, tot, m, p[670000], cnt; //664579

bitset<10000005> vis;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    for (int i = 2; i * i <= maxn; ++i) {
        if (!vis[i]) {
            for (int j = i * i; j <= maxn; j += i)
                vis[j] = 1;
        }
    }

    for (int i = 2; i <= maxn; ++i) {
        if (!vis[i])
            p[++cnt] = i;
    }

    cin >> t;

    for (int ca = 1; ca <= t; ++ca) {
        cin >> k >> n;

        cout << "Case " << ca << ": ";

        if (k == 1) {
            cout << "inf\n";
            continue;
        }

        minx = 9223372036854775807ll;

        for (long long i = 1; i <= cnt && p[i] * p[i] <= k; ++i) {
            if (! (k % p[i])) {
                tot = sum = 0, m = n;

                while (! (k % p[i]))
                    k /= p[i], ++tot;

                while (m)
                    m /= p[i], sum += m;

                minx = min(minx, sum / tot);
            }
        }

        if (k > 1) { // 修改这里，检查k是否为质数，而不是只检查k是否不等于1
            sum = 0;
            m = n;

            while (m)
                m /= k, sum += m;

            minx = min(minx, sum);
        }

        cout << minx << '\n';
    }

    return 0;
}

在这个修改后的版本中，我将这部分代码：

if (k ^ 1) {
    ...
}

更改为：

if (k > 1) {
    ...
}

这样可以确保当k是大于1的质数时也能得到正确的结果。其他部分的代码看起来已经很好了，这个小小的改动应该能解决WA问题。