CF401C题解

题目链接

题意翻译

构造一个 01 序列,包含 n 个 0,m 个 1 要求不存在连续 2 个 0,或 3 个 1 1 <= n; m<=1000000

题目描述

Now it’s time of Olympiads. Vanya and Egor decided to make his own team to take part in a programming Olympiad. They’ve been best friends ever since primary school and hopefully, that can somehow help them in teamwork.

For each team Olympiad, Vanya takes his play cards with numbers. He takes only the cards containing numbers 1 and 0. The boys are very superstitious. They think that they can do well at the Olympiad if they begin with laying all the cards in a row so that:

there wouldn’t be a pair of any side-adjacent cards with zeroes in a row;
there wouldn’t be a group of three consecutive cards containing numbers one.
Today Vanya brought n n cards with zeroes and m m cards with numbers one. The number of cards was so much that the friends do not know how to put all those cards in the described way. Help them find the required arrangement of the cards or else tell the guys that it is impossible to arrange cards in such a way.

输入格式

The first line contains two integers: n n ( 1<=n<=10^{6} 1<=n<=10
6
) — the number of cards containing number 0; m m ( 1<=m<=10^{6} 1<=m<=10
6
) — the number of cards containing number 1.

输出格式

In a single line print the required sequence of zeroes and ones without any spaces. If such sequence is impossible to obtain, print -1.

输入输出样例

输入 #1 复制

1
1 2

输出 #1

1
101

输入 #2

1
4 8

输出 #2

1
110110110101

输入 #3

1
4 10

输出 #3

1
11011011011011

输入 #4

1
1 5

输出 #4

1
-1

题解

首先 将两种特殊情况即输出-1的判断出来
分别是 n > m+1 || m > 2*(n+1)
然后根据不同的情况分类输出即可
代码如下 仅供参考

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#include<iostream>
#include<cstdio>

using namespace std;

int n,m,k,l;

void out()
{
for(int i=1; i<=n; i++)
{
cout<<"10";
}
return ;
}
int main()
{
cin>>n>>m;
if(n>m+1||m>2*(n+1))
{
cout<<"-1";
return 0;
}
if(n==m)
{
out();
return 0;
}
if(n>m)
{
cout<<"0";
n--;
out();
return 0;
}
k=m/2;
while(n>k&&n!=0)
{
cout<<"1";
m--;
cout<<"0";
n--;
k=m/2;
}
l=n;
for(int i=1; i<=n; i++)
{
cout<<"110";
m--;
m--;
l--;
}
if(m==1)
{
cout<<"1";
}
else
{
if(m==2)
{
cout<<"11";
}
}
return 0;
}
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