primeSum.js

function primeSum(n, k) {
    if( k === 1 ){
        return isPrime(n);
    }
    
    var aListPrime = getListPrime(n); 
    log('aListPrime', aListPrime);
    //log('aTable', aTable);
    
    var aListNumber = aListPrime;
    var aTables = [];
    var aTable = {};

    while( k >= 2 ){
        aTable = buidTable(aListNumber, n);
        
        aListNumber = Object.keys(aTable);
        k = k - 2;
        
        // for track
        aTables.push(aTable);
    }
    
    log("k", k);
    log('aTables', aTables);    
    
    if( k===0 ){
        if( aTable[n] !== undefined ){
            console.log("==> found: n =", aTable[n]);
            return true;
        }
        console.log("Not found for ",n);
        return false;
    }
    
    // for k =3, 5
    if( k === 1 ){
        var iLen = aTable.lengh;
        var iTmpl = 0;
        for(var iSum in aTable){
            iTmpl = n - iSum;
            if( aListPrime.indexOf(iTmpl) !== -1 ){
                console.log("==> found: n =", iTmpl, " + ", iSum);
                return true;
            }
        }
        
        console.log("Not found for ",n);
        return false;
    }
}


function log(name, aVal){
    console.log(name," = ", JSON.stringify(aVal, null, 4));
}

function isPrime(n){
    if( n <= 1 )
        return false;
    if( n===2 )
        return true;
    
    var sqrtn = Math.sqrt(n) + 1;
    for(var i = 2; i< sqrtn; i++){
        if( n% i ===0)
            return false;
    }
    return true;
}

function getListPrime(n){
    var aListPrime = [];
    for(var i = 2; i<=n;i++){
       if( isPrime(i) )
           aListPrime.push(i);
    }
    return aListPrime;
}


function buidTable( aListPrime, n ){
    var aTable = {};
    var iLen = aListPrime.length;
    for(var i =0; i< iLen; i++){
        for(var j =0; j< iLen; j++){
            var iSum = parseInt(aListPrime[i]) + parseInt(aListPrime[j]);
            if( iSum <= n ){
                aTable[iSum] = aTable[iSum] || [];
                aTable[iSum].push([aListPrime[i],aListPrime[j]]);
            }
        }
    }
     
    // sort
    iLen = aTable.length;
    for(var i =0; i < iLen; i++){
        for(var j=i+1;j<iLen-1; j++){
            if( aTable[i] > aTable[j] ){
                var aTmpl = aTable[i];
                aTable[i] = aTable[j];
                aTable[i] = aTmpl;
            }
        }
    }
    return aTable;
}
/*
console.clear();
var iStart = (new Date()).getTime();
primeSum(9, 3);
console.info( (new Date()).getTime() - iStart );
*/