← All problems

3751. Total Waviness of Numbers in Range I

MediumOpen on LeetCode Problem statement

Problem Statement

3751. Total Waviness of Numbers in Range I

Medium

You are given two integers num1 and num2 representing an inclusive range [num1, num2].

The waviness of a number is defined as the total count of its peaks and valleys:

A digit is a peak if it is strictly greater than both of its immediate neighbors.
A digit is a valley if it is strictly less than both of its immediate neighbors.
The first and last digits of a number cannot be peaks or valleys.
Any number with fewer than 3 digits has a waviness of 0.

Return the total sum of waviness for all numbers in the range [num1, num2].

Example 1:

Input: num1 = 120, num2 = 130

Output: 3

Explanation:

In the range [120, 130]:

120: middle digit 2 is a peak, waviness = 1.
121: middle digit 2 is a peak, waviness = 1.
130: middle digit 3 is a peak, waviness = 1.
All other numbers in the range have a waviness of 0.

Thus, total waviness is 1 + 1 + 1 = 3.

Example 2:

Input: num1 = 198, num2 = 202

Output: 3

Explanation:

In the range [198, 202]:

198: middle digit 9 is a peak, waviness = 1.
201: middle digit 0 is a valley, waviness = 1.
202: middle digit 0 is a valley, waviness = 1.
All other numbers in the range have a waviness of 0.

Thus, total waviness is 1 + 1 + 1 = 3.

Example 3:

Input: num1 = 4848, num2 = 4848

Output: 2

Explanation:

Number 4848: the second digit 8 is a peak, and the third digit 4 is a valley, giving a waviness of 2.

Constraints:

1 <= num1 <= num2 <= 10⁵

Java — naive

class Solution {
    public int totalWaviness(int num1, int num2) {
        int total = 0;
        for (int i = num1; i <= num2; i++)
            total += waviness(String.valueOf(i));
        return total;
    }

    int waviness(String s) {
        int n = s.length(), wav = 0;
        for (int i = 1; i < n - 1; i++)
            if (s.charAt(i) > Math.max(s.charAt(i - 1), s.charAt(i + 1))
                    || s.charAt(i) < Math.min(s.charAt(i - 1), s.charAt(i + 1)))
                wav++;
        return wav;
    }
}

Java

class Solution {
    public int totalWaviness(int num1, int num2) {
        int total = 0;
        for (int i = num1; i <= num2; i++)
            total += waviness(String.valueOf(i));
        return total;
    }

    int waviness(String s) {
        int n = s.length(), wav = 0;
        for (int i = 1; i < n - 1; i++)
            if (s.charAt(i) > Math.max(s.charAt(i - 1), s.charAt(i + 1))
                    || s.charAt(i) < Math.min(s.charAt(i - 1), s.charAt(i + 1)))
                wav++;
        return wav;
    }
}