project_euler_14.js

 var LIMIT = 1000000;
 var cache = [];
 var output = [1, 1];
 
 for (var i = 0; i < LIMIT; i++) {
     cache[i] = i==1 ? i : 0;
 }
 
 for (i = 1; i < LIMIT; i++) {
     var n = i, ll = 0, Q = [];
 
     while (n > (LIMIT - 1) || cache[n] < 1) {
         ll++;
         Q.push(n);
         n = n%2 == 0 ? n/2 : 3*n+1;
     }
 
     var p = cache[n];
 
     for (var j = 0; j < ll; j++) {
         var m = Q[j];
 
         if (m < LIMIT) {
             newLength = cache[n] + ll - j;
             cache[m] = newLength;
 
             if (newLength > output[1]) output = [i, newLength];
         }
     }
 }
 
 console.log(output);