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🚀 April 25, 2018♻ May 21, 2018reading 9 min reading

Warm-up Challenges ⚡ Counting Valleys

I'm posting about my solutions to the HackerRank challenges as a way to improve my learning, reinforce my knowledge, and establish an understanding of the concepts covered. If I help someone by sharing along the way, even better!

Counting Valleys is one of the initial challenges with 'EASY' difficulty.

What's the challenge?

Gary is an avid climber. It tracks your walks meticulously, paying close attention to small details like topography. During his last walk he took exactly n steps. For each step he took, he noted whether it was an up, U, or a down, D step. Gary's hikes start and end at sea level and each step up or down represents a 1 unit change in altitude. We define the following terms:

  • A mountain is a sequence of consecutive steps above sea level, starting with a rise from sea level and ending with a step to sea level.
  • A valley is a sequence of consecutive steps below sea level, starting with a step below sea level and ending with a step to sea level.

Given Gary's sequence of going up and down the steps during his last walk, find and print the number of valleys he walked. For example, if Gary's path is s = [DDUUUUDD], he will first enter a valley that is 2 units deep. Then he climbs a mountain 2 units high. Finally, he returns to sea level and finishes his walk.

What do we have to do?

A function that should return an integer with the number of valleys traveled by Gary.

  • n = the number of steps Gary walked
  • s = a string describing your path

Sample Input


Sample Output



function countingValleys(n, s) {

	let level = 0,
		valleys = 0,
		i = 0;
	for (i in s) {
		s.charAt(i) === 'U' ? level++ : level--;
		level === 0 && s.charAt(i) === 'U' ? valleys++ : 0;

	return valleys;


let level = 0,
		valleys = 0,
		i = 0;

First I created three variables; level to track altitude; valleys to keep count of the number of valleys Gary has traversed; i to iterate the forloop;

for in

I've created a for loop that will go through the sequence of steps that Gary went through. for (i in s) {

The ternary condition if checks if Gary's step was up U: s.charAt(i) === 'U' ? if was, increment the count: level++ If not, decrement the count. level--

I then check that Gary is at sea level level === 0 and that the step was up && s.charAt(i) === 'U', in this case representing that he has just climbed a valley. valleys++

As at the beginning of the challenge we are informed that Gary starts and ends his walks at sea level, we can ignore knowing if he climbed a mountain and focus only on the valley 😎.

Finally, I finalize the function by returning the final count. 🖖

🕵Extra Solutions

Other languages that I speak

💎 Ruby

def countingValleys(n, s)
	level = 0
	valleys = 0

	s.each { | i | 
		i == 'U' ? level += 1 : level -= 1
		level == 0 && i == 'U' ? valleys += 1 : 0


🐍 PYTHON 2 & 3

def countingValleys(n, s):
	level = 0
	valleys = 0
	for i in range(n):
		if (s[i] == 'U'):
			level += 1
			level -= 1

		if (level == 0 and s[i] == 'U'):
			valleys += 1
	return valleys

golang GOLANG

func countingValleys(n int32, s string) int32 {
	var level, valleys int32
	for _, i := range s {
		if i == 'U' {
		} else {
		if level == 0 && i == 'U' {
	return valleys

scala SCALA

def countingValleys(n: Int, s: String): Int = {
	var level = 0
	var valleys = 0
	s.foreach (el =>  {
		if (el == 'U') {
			level += 1
		} else {
			level -= 1
		if (level == 0 && el == 'U') {
			valleys += 1

	return valleys;

javaJAVA 7 & 8

static int countingValleys(int n, String s) {
	int level = 0,
			valleys = 0;
	for (int i = 0; i < n; i++) {
		if (s.charAt(i) == 'U')
		if (level == 0 && s.charAt(i) == 'U')

	return valleys;

php PHP

function countingValleys($n, $s) {
	$level = 0;
	$count = 0;

	for ($i = 0; $i < $n; $i++) {
		$s[$i] == 'U' ? $level++ : $level--;
		$level == 0 && $s[$i] == 'U' ? $valleys++ : 0;
	return $valleys;

Thought: Nurture your mind with great thoughts, for you will never go any higher than you think.
Benjamin Disraeli

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I don't claim that these answers are the best or most efficient, they are simply creations of my mind to solve the problem at that time. Probably today I would do different...
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