Javascript implemetations for comment https://news.ycombinator.com/item?id=6823433

collatz.js

        function naive(){
        var
            max_a0 = process.argv[2],
            longest = 0,
            max_len = 0, a0,len,a;
        
        for(a0=1;a0<=max_a0;a0++){
            a = a0;
            len = 0;
            while( a != 1){
                len++;
                a = ((a%2==0)? a : 3*a+1)/2;
            }
            if(len>max_len){
                max_len = len;
                longest = a0;
            }
        }
        console.log(max_len,longest);
        }
       
       function intArithm(){
        var
            max_a0 = +process.argv[2],
            longest = 0,
            max_len = 0, a0,len, a,z;

        for(a0=1;a0<=max_a0;++a0){
            a = a0;
            len = 0;
            while( a != 1){
                len++;
                z = a >>> 1;
                a = (!(a&1))?z:(a+z+1);
            }
            if(len>max_len){
                max_len = len;
                longest = a0;
            }
        }
        console.log(max_len,longest);
        }
        
         function intArithmMemo(){
            var
                max_a0 = +process.argv[2],
                longest = 0,
                max_len = 0, a0,len, a, z, mem = {};

            for(a0=1;a0<=max_a0;++a0){
                a = a0;
                len = 0;
                while( a != 1){
                    if(mem[a]){
                        len+=mem[a];
                        break;
                    }
                    len++;
                    z = a >>> 1;
                    a = (!(a&1))?z:(a+z+1);
                    
                }
                mem[a0] = len;
                if(len>max_len){
                    max_len = len;
                    longest = a0;
                }
            }
            console.log(max_len,longest);
        }

        
        var st = Date.now();
        naive();
        console.log('naive',((Date.now()-st)/1000).toFixed(2),'sec');
        
        var st = Date.now();
        intArithm();
        console.log('intArithm',((Date.now()-st)/1000).toFixed(2),'sec');
        
        var st = Date.now();
        intArithmMemo();
        console.log('intArithm memoized',((Date.now()-st)/1000).toFixed(2),'sec');
        
        
        
        function next_collatz(a){
            return ((a%2==0)? a : 3*a+1)/2;
        }
        function len4a(a){
            var len =0;
            while(a!=1){
                len++;
                a = next_collatz(a);
            }
            return len;
        }
        
        var mem = {};
        function mlen4a(a0){
            var len = 0, a = a0;
            while(a!=1){
                if(mem[a]){
                    len+=mem[a];
                    break;
                }
                len++;
                a = next_collatz(a);
            }
            mem[a0] = len;
            return len;
        }
        
        function decompozed(lf){
            var
                max_a0 = process.argv[2],
                longest = 0,
                max_len = 0, a0,len,a;
        
            for(a0=1;a0<=max_a0;a0++){
                len = lf(a0)
                if(len>max_len){
                    max_len = len;
                    longest = a0;
                }
            }
            console.log(max_len,longest);
        }
        var st = Date.now();
        decompozed(len4a);
        console.log('decompozed',((Date.now()-st)/1000).toFixed(2),'sec');
        
        var st = Date.now();
        decompozed(mlen4a);
        console.log('memoized decompozed',((Date.now()-st)/1000).toFixed(2),'sec');