Check if digits of a number are increasing and decreasing alternatively

Last Updated : 27 Jan, 2022

Given a number N, the task is to check whether the digits of the number are increasing and decreasing alternatively. If the number of digits is less than 3, return false. For example, if d1, d2, and d3 are the digits of N, the d1 < d2 > d3, must hold true.
Examples:

Input: N = 6834
Output: true
Explanation: Digits of N are increasing and decreasing alternatively, i.e 6 < 8 > 3 < 4
Input: N = 32
Output: false

Approach: The task can be solved by converting the given integer into a string. Iterate over the string and check whether the adjacent characters follow the given conditions or not.
Below is the implementation of the above approach:

C++

// C++ implementation for the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Utility function to check if
// the digits of the current
// integer forms a wave pattern
bool check(int N)
{
    // Convert the number to a string
    string S = to_string(N);
 
    // Loop to iterate over digits
    for (int i = 0; i < S.size(); i++) {
        if (i == 0) {
 
            // Next character of
            // the number
            int next = i + 1;
 
            // Current character is
            // not a local minimum
            if (next < S.size()) {
                if (S[i] >= S[next]) {
 
                    return false;
                }
            }
        }
 
        else if (i == S.size() - 1) {
 
            // Previous character of
            // the number
            int prev = i - 1;
            if (prev >= 0) {
 
                // Character is a
                // local maximum
                if (i & 1) {
 
                    // Character is not
                    // a local maximum
                    if (S[i] <= S[prev]) {
                        return false;
                    }
                }
                else {
                    // Character is a
                    // local minimum
                    if (S[i] >= S[prev]) {
                        return false;
                    }
                }
            }
        }
        else {
            int prev = i - 1;
            int next = i + 1;
            if (i & 1) {
 
                // Character is a
                // local maximum
                if ((S[i] > S[prev])
                    && (S[i] > S[next])) {
                }
                else {
                    return false;
                }
            }
            else {
                // Character is a
                // local minimum
                if ((S[i] < S[prev])
                    && (S[i] < S[next])) {
                }
                else {
                    return false;
                }
            }
        }
    }
    return true;
}
 
// Driver Code
int main()
{
    int N = 64;
    cout << (check(N) ? "true" : "false");
}

Java

// Java program for the above approach
import java.io.*;
import java.lang.*;
import java.util.*;
 
class GFG {
 
  // Utility function to check if
  // the digits of the current
  // integer forms a wave pattern
  static Boolean check(int N)
  {
     
    // Convert the number to a string
    String S = Integer.toString(N);
 
    // Loop to iterate over digits
    for (int i = 0; i < S.length(); i++) {
      if (i == 0) {
 
        // Next character of
        // the number
        int next = i + 1;
 
        // Current character is
        // not a local minimum
        if (next < S.length()) {
          if (S.charAt(i) >= S.charAt(next)) {
 
            return false;
          }
        }
      }
 
      else if (i == S.length() - 1) {
 
        // Previous character of
        // the number
        int prev = i - 1;
        if (prev >= 0) {
 
          // Character is a
          // local maximum
          if (i % 2 == 1) {
 
            // Character is not
            // a local maximum
            if (S.charAt(i) <= S.charAt(prev)) {
              return false;
            }
          }
          else {
            // Character is a
            // local minimum
            if (S.charAt(i) >= S.charAt(prev)) {
              return false;
            }
          }
        }
      }
      else {
        int prev = i - 1;
        int next = i + 1;
        if (i % 2 == 1) {
 
          // Character is a
          // local maximum
          if ((S.charAt(i) > S.charAt(prev))
              && (S.charAt(i) > S.charAt(next))) {
          }
          else {
            return false;
          }
        }
        else
        {
           
          // Character is a
          // local minimum
          if ((S.charAt(i) < S.charAt(prev))
              && (S.charAt(i) < S.charAt(next))) {
          }
          else {
            return false;
          }
        }
      }
    }
    return true;
  }
 
  // Driver Code
  public static void main (String[] args) {
    int N = 64;
    if(check(N) == true)
      System.out.print("true");
    else
      System.out.print("false");
  }
}
 
// This code is contributed by hrithikgarg03188

Python3

# Python implementation for the above approach
 
# Utility function to check if
# the digits of the current
# integer forms a wave pattern
def check(N):
    # Convert the number to a string
    S = str(N)
 
    # Loop to iterate over digits
    for i in range(len(S)):
        if (i == 0):
 
            # Next character of
            # the number
            next = i + 1
 
            # Current character is
            # not a local minimum
            if (next < len(S)):
                if (S[i] >= S[next]):
                    return False
 
        elif (i == len(S) - 1):
 
            # Previous character of
            # the number
            prev = i - 1
            if (prev >= 0):
 
                # Character is a
                # local maximum
                if (i & 1):
 
                    # Character is not
                    # a local maximum
                    if (S[i] <= S[prev]):
                        return False
                else:
                    # Character is a
                    # local minimum
                    if (S[i] >= S[prev]):
                        return False
        else:
            prev = i - 1
            next = i + 1
            if (i & 1):
 
                # Character is a
                # local maximum
                if ((S[i] > S[prev]) and (S[i] > S[next])):
                    print("", end="")
                else:
                    return False
            else:
                # Character is a
                # local minimum
                if ((S[i] < S[prev]) and (S[i] < S[next])):
                    print("", end="")
                else:
                    return False
    return True
 
 
# Driver Code
 
N = 64
print("true" if check(N) else "false")
 
# This code is contributed by Saurabh Jaiswal

C#

// C# program for the above approach
using System;
 
class GFG {
 
  // Utility function to check if
  // the digits of the current
  // integer forms a wave pattern
  static bool check(int N)
  {
 
    // Convert the number to a string
    string S = N.ToString();
 
    // Loop to iterate over digits
    for (int i = 0; i < S.Length; i++) {
      if (i == 0) {
 
        // Next character of
        // the number
        int next = i + 1;
 
        // Current character is
        // not a local minimum
        if (next < S.Length) {
          if (S[i] >= S[next]) {
 
            return false;
          }
        }
      }
 
      else if (i == S.Length - 1) {
 
        // Previous character of
        // the number
        int prev = i - 1;
        if (prev >= 0) {
 
          // Character is a
          // local maximum
          if (i % 2 == 1) {
 
            // Character is not
            // a local maximum
            if (S[i] <= S[prev]) {
              return false;
            }
          }
          else {
            // Character is a
            // local minimum
            if (S[i] >= S[prev]) {
              return false;
            }
          }
        }
      }
      else {
        int prev = i - 1;
        int next = i + 1;
        if (i % 2 == 1) {
 
          // Character is a
          // local maximum
          if ((S[i] > S[prev])
              && (S[i] > S[next])) {
          }
          else {
            return false;
          }
        }
        else
        {
 
          // Character is a
          // local minimum
          if ((S[i] < S[prev])
              && (S[i] < S[next])) {
          }
          else {
            return false;
          }
        }
      }
    }
    return true;
  }
 
  // Driver Code
  public static void Main () {
    int N = 64;
    if(check(N) == true)
      Console.Write("true");
    else
      Console.Write("false");
  }
}
 
// This code is contributed by Samim Hossain Mondal.

Javascript

<script>
// Javascript implementation for the above approach
 
// Utility function to check if
// the digits of the current
// integer forms a wave pattern
function check(N){
    // Convert the number to a string
    let S = new String(N);
 
    // Loop to iterate over digits
    for (let i = 0; i < S.length; i++) {
        if (i == 0) {
 
            // Next character of
            // the number
            let next = i + 1;
 
            // Current character is
            // not a local minimum
            if (next < S.length) {
                if (S[i] >= S[next]) {
                    return false;
                }
            }
        }
 
        else if (i == S.length - 1) {
 
            // Previous character of
            // the number
            let prev = i - 1;
            if (prev >= 0) {
 
                // Character is a
                // local maximum
                if (i & 1) {
 
                    // Character is not
                    // a local maximum
                    if (S[i] <= S[prev]) {
                        return false;
                    }
                }
                else {
                    // Character is a
                    // local minimum
                    if (S[i] >= S[prev]) {
                        return false;
                    }
                }
            }
        }
        else {
            let prev = i - 1;
            let next = i + 1;
            if (i & 1) {
 
                // Character is a
                // local maximum
                if ((S[i] > S[prev])
                    && (S[i] > S[next])) {
                }
                else {
                    return false;
                }
            }
            else {
                // Character is a
                // local minimum
                if ((S[i] < S[prev])
                    && (S[i] < S[next])) {
                }
                else {
                    return false;
                }
            }
        }
    }
    return true;
}
 
// Driver Code
 
let N = 64;
document.write(check(N) ? "true" : "false");
 
// This code is contributed by gfgking.
</script>