oj上提交后有4个test超时，求如何优化

Question

#include<stdio.h>
#include<string.h>
#define max(m,n) m>n?m:n
int max = 0;
int MyFuction(char str[], int k, int j, int len)
{
	if (k == 0)
	{
		int sum = 0;
		for (int i = 0; i < len; ++i)
		{
			if (str[i] == '1')
			{
				++sum;
				if (str[i + 1] != '1')
					max = max(max, sum);
			}
			else
				sum = 0;
		}
	}
		for (int i = j; i < len&&k>0; ++i)
		{
			if (str[i] =='0')
			{
				str[i] = '1';
				MyFuction(str, k - 1, j + 1, len);
				str[i] = '0';
			}
		}
		return max;
}
int main()
{
	int k;
	char str[100];
	scanf("%s%d", &str, &k);
	int len = strlen(str);
	int sum0 = 0, j = 0;
	for (int i = 0; i < len; ++i)
	{
		if (str[i] == '0')
			++sum0;
	}
	if (k >= sum0)
		printf("%d", len);
	else
		printf("%d", MyFuction(str, k, j, len));
	return 0;
}