Question

Given an array of unsorted positive ints, write a function that finds runs of 3 consecutive numbers (ascending or descending) and returns the indices where such runs begin. If no such runs are found, return null.

function findConsecutiveRuns(input:Array):Array

Example: [1, 2, 3, 5, 10, 9, 8, 9, 10, 11, 7] would return [0, 4, 6, 7]

My JS skills are a bit rusty, here is my attempt at this…

var numArray = [1, 2, 3, 5, 10, 9, 8, 9, 10, 11, 7];
var newNumArray = []; 

for(var i = 1; i < numArray.length; i++) {
    if ((numArray[i] - numArray[i-1] != 1) || (numArray[i] + numArray[i+1] !=1)  {
        return 0;
    }
    else {
    newNumArray.push(numArray[i]);
    }
}
alert(newNumArray);

Answer 1

Here:

function f ( arr ) {
    var diff1, diff2, result = [];

    for ( var i = 0, len = arr.length; i < len - 2; i += 1 ) {
        diff1 = arr[i] - arr[i+1];
        diff2 = arr[i+1] - arr[i+2];
        if ( Math.abs( diff1 ) === 1 && diff1 === diff2 ) {
            result.push( i );
        }        
    }

    return result.length > 0 ? result : null;
}

Live demo: http://jsfiddle.net/Cc4DT/1/