Programming Excercise

general3.js

/*
Exercise:

Write a function that takes in a number N and counts 
how many numbers between 1 and N (inclusive) do not 
contain any digits which are ’7′.
*/


//Recursively, it comes out somewhat nice and clean:
 
function countNumbers(n) {
    var number = n.toString();
    if (n == 1) {
        return 1;
    }
    for (var i = 0; i < number.length; i++) {
        if (number[i] == '7') {
            return countNumbers(n - 1);
        }
    }
    return (countNumbers(n - 1) + 1);
}
 
//But this'll quickly break the stack, given a sufficiently large n.

//A better approach is iteration:
 
function countNumbers(n) {
    var count = 0;
    for (var j = 1; j <= n; j++) {
        count++;
        var number = j.toString();
        for (var i = 0; i < number.length; i++) {
            if (number[i] == '7') {
                count--;
                break;
            }
        }
    }
    return count;
}