排列充电器(Arranging Adapters) 题解

思路分析

按题目要求使用对应数据结构与算法模拟/递推求解，注意数据范围边界与时间复杂度。

参考代码

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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    long long s;
    if (!(cin >> n >> s)) return 0;
    vector<long long> w(n);
    for (int i = 0; i < n; ++i) cin >> w[i];
    sort(w.begin(), w.end());
    auto check = [&](int k) {
        if (k == 0) return true;
        if (s == 1) return k <= 1;
        if (k <= 2) return true;
        long long need = 2;
        long long cnt1 = 0, cnt2 = 0;
        for (int i = 0; i < k - 2; ++i) {
            need += w[i] / 3;
            int r = (int)(w[i] % 3);
            if (r == 1) ++cnt1;
            else if (r == 2) ++cnt2;
        }
        need += cnt2;
        if (cnt1 > cnt2) {
            need += (cnt1 - cnt2 + 1) / 2;
        }
        return need <= s;
    };
    int lo = 0, hi = n, ans = 0;
    while (lo <= hi) {
        int mid = (lo + hi) >> 1;
        if (check(mid)) {
            ans = mid;
            lo = mid + 1;
        } else {
            hi = mid - 1;
        }
    }
    cout << ans << "\n";
    return 0;
}