首个题解

解：

#include <iostream>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
using namespace std;
int sumOfDivisors(int x) {
    int sum = 1; 
    for (int i = 2; i * i <= x; ++i) {
        if (x % i == 0) {
            sum += i;
            if (i != x / i) {
                sum += x / i;
            }
        }
    }
    return sum;
}
int dfs(int num, unordered_map<int, vector<int>>& transform, unordered_set<int>& visited) {
    visited.insert(num);
    int maxSteps = 0;
    for (int nextNum : transform[num]) {
        if (visited.find(nextNum) == visited.end()) {
            int steps = 1 + dfs(nextNum, transform, visited);
            maxSteps = max(maxSteps, steps);
        }
    }
    visited.erase(num); 
    return maxSteps;
}
int main() {
    int n;
    cin >> n;
    unordered_map<int, vector<int>> transform;
    for (int i = 1; i <= n; ++i) {
        int sum = sumOfDivisors(i);
        if (sum < i && sum <= n) {
            transform[i].push_back(sum);
            transform[sum].push_back(i); 
        }
    }
    int maxSteps = 0;
    for (int i = 1; i <= n; ++i) {
        unordered_set<int> visited;
        int steps = dfs(i, transform, visited);
        maxSteps = max(maxSteps, steps);
    }
    cout << maxSteps << endl;
    return 0;
}

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