curriculum/challenges/english/blocks/project-euler-problems-1-to-100/5900f3bb1000cf542c50fece.md
A common security method used for online banking is to ask the user for three random characters from a passcode. For example, if the passcode was 531278, they may ask for the 2nd, 3rd, and 5th characters; the expected reply would be: 317.
The arrays, keylog1, keylog2, and keylog3, contains fifty successful login attempts.
Given that the three characters are always asked for in order, analyze the array so as to determine the shortest possible secret passcode of unknown length.
passcodeDerivation(keylog1) should return a number.
const _keylog1 = [
127,327,178,528,537,538,532,328,127,178,537,127,317,328,512,278,328,327,178,327,578,317,527,178,128,328,517,312,531,128,128,317,527,312,328,532,512,518,317,127,537,528,537,527,327,278,532,128,318,517
];
assert.isNumber(passcodeDerivation(_keylog1));
passcodeDerivation(keylog1) should return 531278.
const _keylog1 = [
127,327,178,528,537,538,532,328,127,178,537,127,317,328,512,278,328,327,178,327,578,317,527,178,128,328,517,312,531,128,128,317,527,312,328,532,512,518,317,127,537,528,537,527,327,278,532,128,318,517
];
assert.strictEqual(passcodeDerivation(_keylog1), 531278);
passcodeDerivation(keylog2) should return 1230567.
const _keylog2 = [
305,367,256,123,357,120,125,307,236,256,356,267,357,256,356,136,257,107,126,567,567,105,120,237,367,120,367,135,207,167,367,367,307,125,120,130,367,230,106,356,126,106,130,123,307,127,306,167,136,126
];
assert.strictEqual(passcodeDerivation(_keylog2), 1230567);
passcodeDerivation(keylog3) should return 73162890.
const _keylog3 = [
319,680,180,690,129,620,762,689,762,318,368,710,720,710,629,168,160,689,716,731,736,729,316,729,729,710,769,290,719,680,318,389,162,289,162,718,729,319,790,680,890,362,319,760,316,729,380,319,728,716,
];
assert.strictEqual(passcodeDerivation(_keylog3), 73162890);
function passcodeDerivation(arr) {
return true;
}
// Only change code above this line
const keylog1 = [
319,680,180,690,129,620,762,689,762,318,368,710,720,710,629,168,160,689,716,731,736,729,316,729,729,710,769,290,719,680,318,389,162,289,162,718,729,319,790,680,890,362,319,760,316,729,380,319,728,716,
];
passcodeDerivation(keylog1);
function passcodeDerivation(arr) {
const numbersInPasscode = [];
const relativePositions = new Array(10)
.fill()
.map(() => new Array(10).fill(0));
for (let i = 0; i < arr.length; i++) {
const curAttempt = arr[i]
.toString()
.split('')
.map(key => parseInt(key, 10));
for (let j = 0; j < curAttempt.length; j++) {
if (numbersInPasscode.indexOf(curAttempt[j]) === -1) {
numbersInPasscode.push(curAttempt[j]);
}
for (let k = j + 1; k < curAttempt.length; k++) {
relativePositions[curAttempt[j]][curAttempt[k]] += 1;
}
}
}
const ranks = {};
for (let i = 0; i < numbersInPasscode.length; i++) {
const curNumber = numbersInPasscode[i];
ranks[curNumber] = relativePositions[curNumber].filter(
count => count > 0
).length;
}
const passcode = numbersInPasscode
.sort((i, j) => ranks[i] - ranks[j])
.reverse()
.join('');
return parseInt(passcode, 10);
}