Print all the peaks and troughs in an Array of Integers - GeeksforGeeks

12 May, 2021
Given an array of integers arr[], the task is to print a list of all the peaks and another list of all the troughs present in the array. A peak is an element in the array which is greater than its neighbouring elements. Similarly, a trough is an element that is smaller than its neighbouring elements.
Examples:  
Input: arr[] = {5, 10, 5, 7, 4, 3, 5} Output: Peaks : 10 7 5 Troughs : 5 5 3Input: arr[] = {1, 2, 3, 4, 5} Output: Peaks : 5 Troughs : 1  
Approach: For every element of the array, check whether the current element is a peak (the element has to be greater than its neighbouring elements) or a trough (the element has to be smaller than its neighbouring elements). Note that the first and the last element of the array will have a single neighbour.
Below is the implementation of the above approach: 
C++
Java
Python3
C#
Javascript
// C++ implementation of the approach#include <iostream>using namespace std; // Function that returns true if num is// greater than both arr[i] and arr[j]static bool isPeak(int arr[], int n, int num,                   int i, int j){     // If num is smaller than the element    // on the left (if exists)    if (i >= 0 && arr[i] > num)        return false;     // If num is smaller than the element    // on the right (if exists)    if (j < n && arr[j] > num)        return false;    return true;} // Function that returns true if num is// smaller than both arr[i] and arr[j]static bool isTrough(int arr[], int n, int num,                     int i, int j){     // If num is greater than the element    // on the left (if exists)    if (i >= 0 && arr[i] < num)        return false;     // If num is greater than the element    // on the right (if exists)    if (j < n && arr[j] < num)        return false;    return true;} void printPeaksTroughs(int arr[], int n){    cout << "Peaks : ";     // For every element    for (int i = 0; i < n; i++) {         // If the current element is a peak        if (isPeak(arr, n, arr[i], i - 1, i + 1))            cout << arr[i] << " ";    }    cout << endl;     cout << "Troughs : ";     // For every element    for (int i = 0; i < n; i++) {         // If the current element is a trough        if (isTrough(arr, n, arr[i], i - 1, i + 1))            cout << arr[i] << " ";    }} // Driver codeint main(){    int arr[] = { 5, 10, 5, 7, 4, 3, 5 };    int n = sizeof(arr) / sizeof(arr[0]);     printPeaksTroughs(arr, n);     return 0;}
// Java implementation of the approachimport java.util.*; class GFG{     // Function that returns true if num is    // greater than both arr[i] and arr[j]    static boolean isPeak(int arr[], int n, int num,                                    int i, int j)    {         // If num is smaller than the element        // on the left (if exists)        if (i >= 0 && arr[i] > num)        {            return false;        }         // If num is smaller than the element        // on the right (if exists)        if (j < n && arr[j] > num)        {            return false;        }        return true;    }     // Function that returns true if num is    // smaller than both arr[i] and arr[j]    static boolean isTrough(int arr[], int n, int num,                                        int i, int j)    {         // If num is greater than the element        // on the left (if exists)        if (i >= 0 && arr[i] < num)        {            return false;        }         // If num is greater than the element        // on the right (if exists)        if (j < n && arr[j] < num)        {            return false;        }        return true;    }     static void printPeaksTroughs(int arr[], int n)    {        System.out.print("Peaks : ");         // For every element        for (int i = 0; i < n; i++)        {             // If the current element is a peak            if (isPeak(arr, n, arr[i], i - 1, i + 1))            {                System.out.print(arr[i] + " ");            }        }        System.out.println("");         System.out.print("Troughs : ");         // For every element        for (int i = 0; i < n; i++)        {             // If the current element is a trough            if (isTrough(arr, n, arr[i], i - 1, i + 1))            {                System.out.print(arr[i] + " ");            }        }    }     // Driver code    public static void main(String[] args)    {        int arr[] = {5, 10, 5, 7, 4, 3, 5};        int n = arr.length;         printPeaksTroughs(arr, n);    }} // This code is contributed by Rajput-Ji
# Python3 implementation of the approach # Function that returns true if num is# greater than both arr[i] and arr[j]def isPeak(arr, n, num, i, j):     # If num is smaller than the element    # on the left (if exists)    if (i >= 0 and arr[i] > num):        return False     # If num is smaller than the element    # on the right (if exists)    if (j < n and arr[j] > num):        return False    return True # Function that returns true if num is# smaller than both arr[i] and arr[j]def isTrough(arr, n, num, i, j):     # If num is greater than the element    # on the left (if exists)    if (i >= 0 and arr[i] < num):        return False     # If num is greater than the element    # on the right (if exists)    if (j < n and arr[j] < num):        return False    return True def printPeaksTroughs(arr, n):     print("Peaks : ", end = "")     # For every element    for i in range(n):         # If the current element is a peak        if (isPeak(arr, n, arr[i], i - 1, i + 1)):            print(arr[i], end = " ")    print()     print("Troughs : ", end = "")     # For every element    for i in range(n):         # If the current element is a trough        if (isTrough(arr, n, arr[i], i - 1, i + 1)):            print(arr[i], end = " ") # Driver codearr = [5, 10, 5, 7, 4, 3, 5]n = len(arr) printPeaksTroughs(arr, n) # This code is contributed by Mohit Kumar
// C# implementation of the approachusing System;     class GFG{     // Function that returns true if num is    // greater than both arr[i] and arr[j]    static Boolean isPeak(int []arr, int n, int num,                                    int i, int j)    {         // If num is smaller than the element        // on the left (if exists)        if (i >= 0 && arr[i] > num)        {            return false;        }         // If num is smaller than the element        // on the right (if exists)        if (j < n && arr[j] > num)        {            return false;        }        return true;    }     // Function that returns true if num is    // smaller than both arr[i] and arr[j]    static Boolean isTrough(int []arr, int n, int num,                                        int i, int j)    {         // If num is greater than the element        // on the left (if exists)        if (i >= 0 && arr[i] < num)        {            return false;        }         // If num is greater than the element        // on the right (if exists)        if (j < n && arr[j] < num)        {            return false;        }        return true;    }     static void printPeaksTroughs(int []arr, int n)    {        Console.Write("Peaks : ");         // For every element        for (int i = 0; i < n; i++)        {             // If the current element is a peak            if (isPeak(arr, n, arr[i], i - 1, i + 1))            {                Console.Write(arr[i] + " ");            }        }        Console.WriteLine("");         Console.Write("Troughs : ");         // For every element        for (int i = 0; i < n; i++)        {             // If the current element is a trough            if (isTrough(arr, n, arr[i], i - 1, i + 1))            {                Console.Write(arr[i] + " ");            }        }    }     // Driver code    public static void Main(String[] args)    {        int []arr = {5, 10, 5, 7, 4, 3, 5};        int n = arr.Length;         printPeaksTroughs(arr, n);    }} // This code is contributed by Princi Singh
<script> // Function that returns true if num is// greater than both arr[i] and arr[j]function isPeak(arr, n, num, i,  j){     // If num is smaller than the element    // on the left (if exists)    if (i >= 0 && arr[i] > num)        return false;     // If num is smaller than the element    // on the right (if exists)    if (j < n && arr[j] > num)        return false;    return true;} // Function that returns true if num is// smaller than both arr[i] and arr[j]function isTrough( arr, n,  num, i,  j){     // If num is greater than the element    // on the left (if exists)    if (i >= 0 && arr[i] < num)        return false;     // If num is greater than the element    // on the right (if exists)    if (j < n && arr[j] < num)        return false;    return true;} function printPeaksTroughs( arr, n){    document.write(  "Peaks : ");     // For every element    for (var i = 0; i < n; i++) {         // If the current element is a peak        if (isPeak(arr, n, arr[i], i - 1, i + 1))            document.write( arr[i] + " ");    }    document.write( "<br>");     document.write(  "Troughs : ");     // For every element    for (var i = 0; i < n; i++) {         // If the current element is a trough        if (isTrough(arr, n, arr[i], i - 1, i + 1))            document.write( arr[i] + " ");    }}var arr=[ 5, 10, 5, 7, 4, 3, 5 ];     printPeaksTroughs(arr, 7);     </script>
Peaks : 10 7 5 
Troughs : 5 5 3
 
mohit kumar 29
Rajput-Ji
princi singh
akshitsaxenaa09
Traversal
Arrays
Python
Arrays
Traversal
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