Codeforces Round #604 (Div. 2) D. Beautiful Sequence(构造)

链接：

https://codeforces.com/contest/1265/problem/D

题意：

An integer sequence is called beautiful if the difference between any two consecutive numbers is equal to 1. More formally, a sequence s1,s2,…,sn is beautiful if |si−si+1|=1 for all 1≤i≤n−1.

Trans has a numbers 0, b numbers 1, c numbers 2 and d numbers 3. He wants to construct a beautiful sequence using all of these a+b+c+d numbers.

However, it turns out to be a non-trivial task, and Trans was not able to do it. Could you please help Trans?

思路：

考虑0只能和1，3只能和2，贪心的以01， 23去放，这样0必须小于等于1， 2和3同理，再往中间插21，如果剩下的2和1相差超过1就不能满足条件。

多一个可以插在开头或者结尾。还要考虑0和1为0，2和3为0的特殊情况。

好像暴力枚举也可以。。

代码：

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

int a, b, c, d;

int main()
{
    cin >> a >> b >> c >> d;
    if (((d != 0 || c != 0) && a > b) || ((a != 0 || b != 0) && d > c))
    {
        puts("NO\n");
        return 0;
    }
    if (a == 0 && b == 0)
    {
        if (abs(d-c) > 1)
        {
            puts("NO\n");
            return 0;
        }
        else
        {
            string res = "";
            for (int i = 1;i <= min(c, d);i++)
                res += "23";
            if (c > d)
                res += "2";
            else if (c < d)
                res = "3"+res;
            cout << "YES" << endl;
            for (int i = 0;i < res.length();i++)
                cout << res[i] << ' ';
            cout << endl;
            return 0;
        }
    }
    if (c == 0 && d == 0)
    {
        if (abs(a-b) > 1)
        {
            puts("NO\n");
            return 0;
        }
        else
        {
            string res = "";
            for (int i = 1;i <= min(a, b);i++)
                res += "01";
            if (a > b)
                res += "0";
            else if (a < b)
                res = "1"+res;
            cout << "YES" << endl;
            for (int i = 0;i < res.length();i++)
                cout << res[i] << ' ' ;
            cout << endl;
            return 0;
        }

    }
    int l = b-a, r = c-d;
    if (abs(l-r) > 1)
    {
        puts("NO\n");
        return 0;
    }
    string res = "";
    if (l-r == 1)
        res += "1";
    for (int i = 1;i <= a;i++)
        res += "01";
    for (int i = 1;i <= min(l, r);i++)
        res += "21";
    for (int i = 1;i <= d;i++)
        res += "23";
    if (r-l == 1)
        res += "2";
    cout << "YES" << endl;
    for (int i = 0;i < res.length();i++)
        cout << res[i] << ' ';
    cout << endl;

    return 0;
}