CF962D Merge Equals

思路：

不必每次都找最小的值进行合并，从前往后扫一遍的过程中能合并就一直合并。

实现：

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 150005;
ll a[MAXN];
int main()
{
    int n;
    while (cin >> n)
    {
        map<ll, int> mp;
        for (int i = 0; i < n; i++)
        {
            cin >> a[i];
            if (mp.count(a[i])) 
            { 
                while (mp.count(a[i]))
                {
                    a[mp[a[i]]] = -1;
                    mp.erase(a[i]);
                    a[i] <<= 1;
                }
            }
            mp[a[i]] = i;
        }
        vector<ll> v;
        for (int i = 0; i < n; i++)
        {
            if (a[i] != -1) v.push_back(a[i]);
        }
        cout << v.size() << endl;
        for (int i = 0; i < v.size(); i++) cout << v[i] << " ";
        cout << endl;
    }
    return 0;
}