Hackerrank | Counting Valleys

An avid hiker keeps meticulous records of their hikes. During the last hike that took exactly  steps, for every step it was noted if it was an uphill, U, or a downhill D,  step. Hikes always start and end at sea level, and each step up or down represents 1 a  unit change in altitude. We define the following terms:

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

Given the sequence of up and down steps during a hike, find and print the number of valleys walked through.

Example

steps=8 path=[DDUUUDD]

The hiker first enters a valley 2 units deep. Then they climb out and up onto a mountain 2 units high. Finally, the hiker returns to sea level and ends the hike.

Function Description

Complete the countingValleys function in the editor below.

countingValleys has the following parameter(s):

• int steps: the number of steps on the hike
• string path: a string describing the path

Returns

• int: the number of valleys traversed

Input Format

The first line contains an integer , the number of steps in the hike.
The second line contains a single string , of  characters that describe the path.

Constraints

• 2<=STEPS<=10^6
• PATH[i] belongs to {UD}

Sample Input

8
UDDDUDUU

Sample Output

1

Explanation

If we represent _ as sea level, a step up as /, and a step down as \, the hike can be drawn as:

_/\      _
   \    /
    \/\/

The hiker enters and leaves one valley.

Python Implementation

#!/bin/python3

import math
import os
import random
import re
import sys

#
# Complete the 'countingValleys' function below.
#
# The function is expected to return an INTEGER.
# The function accepts following parameters:
#  1. INTEGER steps
#  2. STRING path
#

def countingValleys(steps, path):
    level = 0  # Initialize altitude level
    valleys = 0  # Initialize the number of valleys

    for step in path:
        if step == 'U':
            level += 1
        elif step == 'D':
            level -= 1

        # Check for a valley (step up from below sea level to sea level)
        if step == 'U' and level == 0:
            valleys += 1

    return valleys
    # Write your code here

if __name__ == '__main__':
    fptr = open(os.environ['OUTPUT_PATH'], 'w')

    steps = int(input().strip())

    path = input()

    result = countingValleys(steps, path)

    fptr.write(str(result) + '\n')

    fptr.close()

C Implementation

#include <stdio.h>

int countingValleys(int steps, char path[]) {
    int level = 0;  // Initialize altitude level
    int valleys = 0;  // Initialize the number of valleys

    for (int i = 0; i < steps; i++) {
        char step = path[i];

        if (step == 'U') {
            level += 1;
        } else if (step == 'D') {
            level -= 1;
        }

        // Check for a valley (step up from below sea level to sea level)
        if (step == 'U' && level == 0) {
            valleys += 1;
        }
    }

    return valleys;
}

int main() {
    // Example usage:
    int steps = 8;
    char path[] = "UDDDUDUU";

    int result = countingValleys(steps, path);
    printf("%d\n", result);

    return 0;
}