Multiplying all numbers in two arrays in javascript

Question

As an exercise, I'm trying to create a function that returns the palindromic numbers resulting from multiplying three-digit numbers. As far as I can tell, the function is running through numbers correctly, however, the resulting array is incorrect. I don't need the solution to the palindrome problem...just an idea of what I might be missing. Have I run into some limitation?

var palindromic = function() {
var a = [];
var res = [];
for (var i = 100; i < 1000; i++) {
    a.push(i);
}
var ar = a.slice(0);
a.map(function(x) {
    for (var j = 0; j < ar.length; j++) {
        var result = x * ar[j];
        if (result.toString() ===   result.toString().split("").reverse().join("")) {
            res.push(result);
        }
    }
  })
return res;
};

I just noticed that when I change the function to multiply all numbers between 0 and 99 instead of 100 and 999 it works properly. ?? — Ja5onHoffman
– Ja5onHoffman, Commented Oct 24, 2013 at 22:52

Tom Lagier · Accepted Answer · 2013-10-24 21:56:54Z

1

Pretty sure it's just trying to call console.log() 810,000 times. If you comment the console.log line, it works just fine.

var palindromic = function() {
var a = [];
var res = [];
for (var i = 100; i < 1000; i++) {
    a.push(i);
}
var ar = a.slice(0);
a.map(function(x) {
    for (var j = 0; j < ar.length; j++) {
        var result = x * ar[j];
        //console.log(x + " : " + ar[j] + ' = ' + result);
        if (result.toString() ===   result.toString().split("").reverse().join("")) {
            res.push(result);
        }
    }
});
return res;
};

console.log(palindromic());

answered Oct 24, 2013 at 21:56

Tom Lagier

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5 Comments

Ja5onHoffman Over a year ago

That was just to see if it was looping properly. The highest number in the array ends up being 99,999, however, the numbers should go into the 100,000s.

Tom Lagier Over a year ago

From this fiddle, I'm getting 906,609 as the largest. Array.map may not traverse in-order, so res has no guarantee of being ordered.

chsh Over a year ago

Similar to Tom, if I run this code changing the initial array definition to between 900 to < 1000, I get the following numbers, all in the 100,000s: 819918, 824428, 819918, 906609, 824428, 886688, 861168, 888888, 861168, 888888, 886688, 906609

Ja5onHoffman Over a year ago

It worked for me as well when I changed the array definition. Do you know why that is? The 100 to < 1000 version, even when sorted, doesn't contain numbers larger than 99,999.

Tom Lagier Over a year ago

I'm confused on that assertion - the fiddle clearly logs 906,609 as the largest, which I believe is the correct answer to the question "what is the largest palindrome number less than 1,000,000". How are you compiling this? Node, browser, website?

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