最长公共前缀

char *longestCommonPrefix(char **strs, int strsSize)
{    
	if(strsSize==0)    
	{        
		return "";    
	}    
	char *str;    
	int i,j = 0,num = strlen(strs[0]),n;    
	for(i=1;i<strsSize;i++)    
	{           
		j = 0;        
		while(strs[0][j]==strs[i][j] && strs[0][j]!='\0')        	
		{            
			j++;        
		}        
		if(num>j)       
		{            
			num = j;        
		}    
	}    
	str = (char*)malloc(sizeof(char)*(num + 1));    
	for(n=0;n<num;n++)    
	{        
		str[n] = strs[0][n];    
	}    
	str[n] = '\0';    
	return str;
}