<apex:page controller="AccountTable" sidebar="false" showHeader="false" >
    <apex:form id="myform">
        <apex:pageBlock >
           Please Select A Dealer To Add As Participating Dealer : <apex:selectList value="{!regionValue}" size="1" >
           <apex:actionSupport event="onchange" action="{!dropDown}" rerender="myform"/>
           <apex:selectOptions value="{!regionOptions}"/> 
           </apex:selectList>
        </apex:pageBlock>
        <apex:pageBlock id="table" rendered="{!if(panelStopper = true,true,false)}">
            Filter 
           <p> Dealer Type     <apex:inputText value="{!dealerType}"/> </p>
           <p>  Dealer Code    <apex:inputText value="{!dealerCode}"/> </p>
            <apex:pageBlockButtons location="Bottom">
                <apex:commandButton value="Search" action="{!SearchLogic}" reRender="myform" />
            </apex:pageBlockButtons>
        </apex:pageBlock>

        <apex:outputPanel id="accounts">
            <apex:pageblock >
                <apex:pageblocktable value="{!Account}" var="cc" id="page">
                    <apex:column headerValue="Choose Account">
                        <apex:inputCheckbox value="{!cc.bool}"/>
                    </apex:column><apex:column value="{!cc.con.Name}"/>
                    <apex:column value="{!cc.con.City__c}"/>
                    <apex:column value="{!cc.con.Dealer_GC_Code__c }"/>
                    <apex:column value="{!cc.con.Phone  }"/>
                </apex:pageblocktable>
                <apex:pageBlockButtons location="Bottom">
                    <apex:commandButton value="<<" action="{!first}" reRender="accounts" />
                    <apex:commandButton value="<" action="{!previous}" reRender="accounts" />
                    <apex:commandButton value=">" action="{!next}" reRender="accounts" />
                    <apex:commandButton value=">>" action="{!last}" reRender="accounts" />
                </apex:pageBlockButtons>
                <apex:outputText >Page Number {!pageNumber} </apex:outputText>
                <apex:pageBlockButtons location="bottom">
                    <apex:commandButton value="Add" action="{!clickMe}" />
                    <apex:commandButton value="Cancel"  onclick="window.parent.box.hide()" /> 
                </apex:pageBlockButtons>
            </apex:pageblock>
        </apex:outputPanel>
        <apex:pageblock >
            <apex:outputPanel rendered="{!display}">
                <apex:pageblocktable value="{!selectedList}" var="w" >
                    <apex:column value="{!w.Name}"/>
                </apex:pageblocktable>
            </apex:outputPanel>
        </apex:pageblock>
    </apex:form>
</apex:page>

Public class AccountTable{
    public String size { get; set; }

    //This is Our collection of the class/wrapper objects AddingParticipatingDealer 
    Public List<AddingParticipatingDealer> wrapperlist{get;set;}
    Public Integer noOfRecords{get; set;}

    // Create a new Map to verify whether the Account is already added in the Map
    Map <id,Account> SelectedAccountMap = new Map <id,Account>();

    public boolean display{get;set;}
    public list<Account> selectedList {get;set;}
    public String regionValue {get;set;}    
    public List<SelectOption> regionOptions {get;set;}
    public String dealerType {get;set;}
    public String dealerCode {get;set;} 
    public Boolean panelStopper {get;set;}

    public AccountTable(){ 
        regionOptions = new List<SelectOption>();
        regionOptions.add(new SelectOption('aid','All Dealer'));
        regionOptions.add(new SelectOption('sid','Select A Dealer'));
        panelStopper = false;
    }
    
    public ApexPages.StandardSetController setCon {get;set;}

    //Returns a list of wrapper objects for the sObjects in the current page set
    Public Void dropDown(){
        if(regionValue == 'sid' ){
            panelStopper = true;
        } 
        else{
            panelStopper = false;
        }
    }

    Public void SearchLogic(){
        Setcon = new ApexPages.StandardSetController(Database.getQueryLocator([Select Name,Dealer_Type__c,Dealer_GC_Code__c from Account Where Dealer_Type__c = :dealerType AND Dealer_GC_Code__c=:dealerCode]));
        setCon.setpagesize(10);
        noOfRecords = setCon.getResultSize();
        getAccount();
    }
    
    Public List<AddingParticipatingDealer> getAccount(){
        getSelectedAccount();
        wrapperlist = new List <AddingParticipatingDealer >();
        for(Account cc : (List<Account>)Setcon.getRecords()){ //In debug log it was showing error at this line
            AddingParticipatingDealer wrapAcc = new AddingParticipatingDealer();
            wrapAcc.con = cc;               // Holding Account
            if(SelectedAccountMap.containsKey(cc.Id)){
                wrapAcc.bool = true;    // check if Checkbox is checked in vf page    
            }
            else{
                wrapAcc.bool = false;    // Used as Checkbox in vf page, default is not selected
            }
            wrapperlist.add(wrapAcc);
        }
        return wrapperlist;
    }

    public void getSelectedAccount(){
        if(wrapperlist!=null){
            for(AddingParticipatingDealer  wr:wrapperlist){
                if(wr.bool == true){
                    SelectedAccountMap.put(wr.con.id,wr.con); // Add the selected Account id in to 
                }
                else{
                    SelectedAccountMap.remove(wr.con.id); // If you uncheck the Account, remove it from the selectedAccountMap
                }
            }

        }

    }
    
    public void first(){
        Setcon.first();
        system.debug('++++++++++++++First'+Setcon);
    }
     
     // returns the last page of records
     public void last() {
         Setcon.last();
     }
    
    // returns the previous page of records
     public void previous() {
         Setcon.previous();
     }
    
    //disable first and prev button
    public Boolean hasPrevious {
        get {
            return Setcon.getHasPrevious();
        }
        set;
    }
    
    //display the next page of records
    public void next() {
        Setcon.next();
        system.debug('++++++++++++++Next'+Setcon);
    }
    
    //disable the next and last buttons
    public Boolean hasnext {
        get {
            return Setcon.getHasNext();
        }
        set;
    }

    public void clickMe(){
        display = true;
        getSelectedAccount();
        selectedList = SelectedAccountMap.values();
    }

    public integer pageNumber{
        get{
            return Setcon.getPageNumber();
        }
        set;
    }
    
    Public class AddingParticipatingDealer{
        Public Account con{get;set;}
        Public boolean bool{get;set;}
    }
}

<apex:page controller="AccountTable" sidebar="false" showHeader="false" >
    <apex:form id="myform">
        <apex:pageBlock >
           Please Select A Dealer To Add As Participating Dealer : <apex:selectList value="{!regionValue}" size="1" >
           <apex:actionSupport event="onchange" action="{!dropDown}" rerender="myform"/>
           <apex:selectOptions value="{!regionOptions}"/> 
           </apex:selectList>
        </apex:pageBlock>
        <apex:pageBlock id="table" rendered="{!if(panelStopper = true,true,false)}">
            Filter 
           <p> Dealer Type     <apex:inputText value="{!dealerType}"/> </p>
           <p>  Dealer Code    <apex:inputText value="{!dealerCode}"/> </p>
            <apex:pageBlockButtons location="Bottom">
                <apex:commandButton value="Search" action="{!SearchLogic}" reRender="myform" />
            </apex:pageBlockButtons>
        </apex:pageBlock>

        <apex:outputPanel id="accounts">
            <apex:pageblock >
                <apex:pageblocktable value="{!Account}" var="cc" id="page">
                    <apex:column headerValue="Choose Account">
                        <apex:inputCheckbox value="{!cc.bool}"/>
                    </apex:column><apex:column value="{!cc.con.Name}"/>
                    <apex:column value="{!cc.con.City__c}"/>
                    <apex:column value="{!cc.con.Dealer_GC_Code__c }"/>
                    <apex:column value="{!cc.con.Phone  }"/>
                </apex:pageblocktable>
                <apex:pageBlockButtons location="Bottom">
                    <apex:commandButton value="<<" action="{!first}" reRender="accounts" />
                    <apex:commandButton value="<" action="{!previous}" reRender="accounts" />
                    <apex:commandButton value=">" action="{!next}" reRender="accounts" />
                    <apex:commandButton value=">>" action="{!last}" reRender="accounts" />
                </apex:pageBlockButtons>
                <apex:outputText >Page Number {!pageNumber} </apex:outputText>
                <apex:pageBlockButtons location="bottom">
                    <apex:commandButton value="Add" action="{!clickMe}" />
                    <apex:commandButton value="Cancel"  onclick="window.parent.box.hide()" /> 
                </apex:pageBlockButtons>
            </apex:pageblock>
        </apex:outputPanel>
        <apex:pageblock >
            <apex:outputPanel rendered="{!display}">
                <apex:pageblocktable value="{!selectedList}" var="w" >
                    <apex:column value="{!w.Name}"/>
                </apex:pageblocktable>
            </apex:outputPanel>
        </apex:pageblock>
    </apex:form>
</apex:page>

Public class AccountTable{
    public String size { get; set; }

    //This is Our collection of the class/wrapper objects AddingParticipatingDealer 
    Public List<AddingParticipatingDealer> wrapperlist{get;set;}
    Public Integer noOfRecords{get; set;}

    // Create a new Map to verify whether the Account is already added in the Map
    Map <id,Account> SelectedAccountMap = new Map <id,Account>();

    public boolean display{get;set;}
    public list<Account> selectedList {get;set;}
    public String regionValue {get;set;}    
    public List<SelectOption> regionOptions {get;set;}
    public String dealerType {get;set;}
    public String dealerCode {get;set;} 
    public Boolean panelStopper {get;set;}

    public AccountTable(){ 
        regionOptions = new List<SelectOption>();
        regionOptions.add(new SelectOption('aid','All Dealer'));
        regionOptions.add(new SelectOption('sid','Select A Dealer'));
        panelStopper = false;
    }
    
    public ApexPages.StandardSetController setCon {get;set;}

    //Returns a list of wrapper objects for the sObjects in the current page set
    Public Void dropDown(){
        if(regionValue == 'sid' ){
            panelStopper = true;
        } 
        else{
            panelStopper = false;
        }
    }

    Public void SearchLogic(){
        Setcon = new ApexPages.StandardSetController(Database.getQueryLocator([Select Name,Dealer_Type__c,Dealer_GC_Code__c from Account Where Dealer_Type__c = :dealerType AND Dealer_GC_Code__c=:dealerCode]));
        setCon.setpagesize(10);
        noOfRecords = setCon.getResultSize();
        getAccount();
    }
    
    Public List<AddingParticipatingDealer> getAccount(){
        getSelectedAccount();
        wrapperlist = new List <AddingParticipatingDealer >();
        for(Account cc : (List<Account>)Setcon.getRecords()){ //In debug log it was showing error at this line
            AddingParticipatingDealer wrapAcc = new AddingParticipatingDealer();
            wrapAcc.con = cc;               // Holding Account
            if(SelectedAccountMap.containsKey(cc.Id)){
                wrapAcc.bool = true;    // check if Checkbox is checked in vf page    
            }
            else{
                wrapAcc.bool = false;    // Used as Checkbox in vf page, default is not selected
            }
            wrapperlist.add(wrapAcc);
        }
        return wrapperlist;
    }

    public void getSelectedAccount(){
        if(wrapperlist!=null){
            for(AddingParticipatingDealer  wr:wrapperlist){
                if(wr.bool == true){
                    SelectedAccountMap.put(wr.con.id,wr.con); // Add the selected Account id in to 
                }
                else{
                    SelectedAccountMap.remove(wr.con.id); // If you uncheck the Account, remove it from the selectedAccountMap
                }
            }

        }

    }
    
    public void first(){
        Setcon.first();
        system.debug('++++++++++++++First'+Setcon);
    }
     
     // returns the last page of records
     public void last() {
         Setcon.last();
     }
    
    // returns the previous page of records
     public void previous() {
         Setcon.previous();
     }
    
    //disable first and prev button
    public Boolean hasPrevious {
        get {
            return Setcon.getHasPrevious();
        }
        set;
    }
    
    //display the next page of records
    public void next() {
        Setcon.next();
        system.debug('++++++++++++++Next'+Setcon);
    }
    
    //disable the next and last buttons
    public Boolean hasnext {
        get {
            return Setcon.getHasNext();
        }
        set;
    }

    public void clickMe(){
        display = true;
        getSelectedAccount();
        selectedList = SelectedAccountMap.values();
    }

    public integer pageNumber{
        get{
            return Setcon.getPageNumber();
        }
        set;
    }
    
    Public class AddingParticipatingDealer{
        Public Account con{get;set;}
        Public boolean bool{get;set;}
    }
}