Gragh - 6 months ago 21

Javascript Question

I'm trying to find the various possibilities to equal 100 with digits 1-9. This function produces the desired results, but also others which I had not intended. The other results add up to 100, but without some of these digits, like leaving out 3 or 6. Why are these other results included?

`var nums = [1, 2, 3, 4, 5, 6, 7, 8, 9];`

var signs = ["+", "-", "N"];

var results = [];

find100("1");

function find100(expr) {

if (eval(expr.replace(/N/g, "")) === 100) {

results.push(expr);

} else {

for (var i = eval(expr.substring(expr.length - 1, expr.length)) + 1; i <=

nums.length; i++) {

signs.forEach(function(sign) {

var expr2 = expr;

find100(expr2 += sign + i);

});

}

}

}

Desired output:

`1+2+3-4+5+6+78+9,`

1+2+34-5+67-8+9,

1+23-4+5+6+78-9,

1+23-4+56+7+8+9,

12+3+4+5-6-7+89,

12+3-4+5+67+8+9,

12-3-4+5-6+7+89,

123+4-5+67-89,

123+45-67+8-9,

123-4-5-6-7+8-9,

123-45-67+89

Answer

It's adding undesired results because your first loop iterates through each of the remaining numbers and adds ANY results that evaluate to 100, even if it has skipped a number to do so. If the method finds a solution for a number it adds the solution to `results`

- which is correct, however if it doesn't find a solution it moves onto the next number anyway. This is the source of the skipped numbers. If there was no solution for a number it should have not continued to the next number.

As to how to fix it, that's a different question (but why not ...)

The difference here is that you can ONLY get a result if for any number there exists an expression that uses all remaining numbers.

```
var results = [];
var operations = [ "+", "-", "" ];
var expected = 100;
var limit = 10;
function findExpression(expr, next) {
if (next === limit) {
eval(expr) === expected && results.push(expr);
} else {
operations.forEach(function(operation) {
findExpression(expr + operation + next, next + 1);
});
}
}
$(document).ready(function() {
findExpression("1", 2);
for(var i=0; i<results.length; i++) {
$("#foo").append(results[i]+"<br />");
}
});
```

```
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<body>
<div id="foo"></div>
</body>
```