# Code Corner: Triangles  For the last two weeks, I’ve had a bunch of interviews and code challenge tasks I was taking which took up a lot of my time. Add that to #DadLife and the result is two weeks with no content. The pressure is off for the moment so I’m picking it up again. So for today:

### Problem

We are given an N length array with numbers ranging between a few negative million to a few positive million. If there exists at least one 3-tuple (P, Q, R) combination of values that satisfy the conditions below, return 1 otherwise return 0.

#### Conditions

• The values A, B, C represent indices of A
• 0 <= P < Q < R < N
• A[P] + A[Q] > A[R]
• A[P] + A[R] > A[Q]
• A[R] + A[Q] > A[P]

## My Solution

#### Brute forcing…

The brute force approach worked ok, but as usual didn’t make the performance tests.

Here we have to check a few conditions.

• First and easiest, A[P] should always be less than the sum of A[Q] and A[R]. `a < b + c`
• Second A[P] should be greater than A[Q] – A[R] and A[P] should be greater than A[R] – A[Q], we get these from solving the equations we get in the conditions and can combine the two into one check `a > Math.abs(b - c)`

And thus our first attempt looks like:

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```function brute_force(A) {
const isTriangle = (a, b, c) => {
return a > Math.abs(b - c) && a < b + c
}
if (A.length < 3) {
return 0
}
for (let i = 0; i < A.length - 2; i++) {
for (let j = i + 1; j < A.length - 1; j++) {
for (let k = j + 1; k < A.length; k++) {
if (isTriangle(A[i], A[j], A[k])) {
return 1
}
}
}
}
return 0
}
```Code language: JavaScript (javascript)```

#### Improved Solution

We are obviously looping too much. So I decided to optimise this by first introducing a sort. This should then hopefully reduce it down to one loop. Here is where I made a terrible mistake that messed me up for the better part of 2 hours.

Do you see that condition that checks if our three numbers match our conditions? Yeah, when switching to a sorted approach I was using I as my iterating variable and accidentally inserted 1 instead of i on one of my conditions. So instead of this:

``````if (A[i] > Math.abs(A[i + 1] - A[i + 2]) && A[i] < A[i + 1] + A[i + 2]) {
return 1
}
```Code language: JavaScript (javascript)```

``````if (A[i] > Math.abs(A[i + 1] - A[1 + 2]) && A[i] < A[i + 1] + A[1 + 2]) {
return 1
}
```Code language: JavaScript (javascript)```

If you can’t see the difference, welcome to the club. So it passed a few local tests by happy accident but wouldn’t pass the larger tests. I spent a lot of time trying to figure out what was wrong until I was pulling my locks out. Then after a little break, I came back and saw it.

Correcting the typo fixed the issue and the code passed everything.

``````function solution(A) {
if (A.length < 3) {
return 0
}
A.sort((a, b) => a - b)

for (let i = 0; i < A.length - 2; i++) {
if (A[i] > Math.abs(A[i + 1] - A[i + 2]) && A[i] < A[i + 1] + A[i + 2]) {
return 1
}
}
return 0
}
```Code language: JavaScript (javascript)```

Typos are evil.