Codeforces Round #386 (Div. 2) D - Green and Black Tea

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本文介绍了一个有趣的算法问题，主人公Innokentiy喜欢喝茶，但不愿意连续喝太多相同的茶。文章探讨了如何通过算法确定泡茶的最佳顺序，使得他可以在不违反个人喜好的前提下享受每一杯茶。

Innokentiy likes tea very much and today he wants to drink exactly n cups of tea. He would be happy to drink more but he had exactly n tea bags, a of them are green and b are black.

Innokentiy doesn't like to drink the same tea (green or black) more than k times in a row. Your task is to determine the order of brewing tea bags so that Innokentiy will be able to drink n cups of tea, without drinking the same tea more than k times in a row, or to inform that it is impossible. Each tea bag has to be used exactly once.

Input

The first line contains four integers n, k, a and b (1 ≤ k ≤ n ≤ 105, 0 ≤ a, b ≤ n) — the number of cups of tea Innokentiy wants to drink, the maximum number of cups of same tea he can drink in a row, the number of tea bags of green and black tea. It is guaranteed that a + b = n.

Output

If it is impossible to drink n cups of tea, print "NO" (without quotes).

Otherwise, print the string of the length n, which consists of characters 'G' and 'B'. If some character equals 'G', then the corresponding cup of tea should be green. If some character equals 'B', then the corresponding cup of tea should be black.

If there are multiple answers, print any of them.

Examples

input
5 1 3 2

output
GBGBG

input
7 2 2 5

output
BBGBGBB

input
4 3 4 0

output
NO

思路：先将数量多的放置，再以k个为间隔插入数量少的，如果最后有剩余，再做处理。

代码如下：

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

char str[10000600];

int main()
{
	int n,k,a,b;
	char aa,bb;
	int flag;
	while(~scanf("%d%d%d%d",&n,&k,&a,&b))
	{
		aa='G'; bb='B';	//a cun xiao
		if(a>b)
		{
			swap(a,b);
			swap(aa,bb);
		}
		for(int i=0;i<n;i++)
			str[i]=bb;
		flag=0;
		for(int i=k;i<n;i+=k+1)
		{
			if(a>0)
			{
				str[i]=aa;
				a--;
			}
			else
			{
				flag=1;
			}
		}
		if(!flag)
		{
			for(int i=0;i<n;i++)
			{
				if(a==0)
					break;
				if(str[i]==aa || (i>0 && str[i-1]==aa) || (i+1<n && str[i+1]==aa))
					continue;
				str[i]=aa;
				a--;
			}
			for(int i=0;i<n;i++)
				printf("%c",str[i]);
			printf("\n");
		}
		else
			printf("NO\n");
	}
	
	return 0;
}