Recuento de elementos de array que es más pequeño que sus dos elementos adyacentes

Dada una array arr[] de tamaño N , la tarea es encontrar el número de puntos valle en la array.

Punto de valle: cualquier elemento de la array se conoce como punto de valle si es más pequeño que sus dos elementos adyacentes, es decir  .

Ejemplos:  

Entrada: arr[] = {3, 2, 5} 
Salida: 1 
Explicación: 
Solo hay un punto de valle. Eso es arr[1].

Entrada: arr[] = {5, 4, 8, 3, 6} 
Salida: 2 
Explicación: 
Hay dos puntos de valle. Eso es arr[1] y arr[3]. 
 

Enfoque: la idea es iterar sobre la array desde 1 hasta  y para cada elemento, verificar si ese elemento es un punto de valle o no, si es así, luego incrementar el recuento del punto de valle en 1.

if (arr[i-1] > arr[i] < arr[i])
     count += 1;

A continuación se muestra la implementación del enfoque anterior:

// C++ program to count the number
// of valley points in the array
#include<bits/stdc++.h>
using namespace std;
 
// Function to count the valley points
// in the given character array
int countValleys(int n, int arr[])
{
    int count = 0, temp = 0;
     
    // Loop to iterate over the
    // elements of the given array
    for(int i = 1; i < n - 1; i++)
    {
        
       // Condition to check if the given
       // element is a valley point
       if (arr[i - 1] > arr[i] &&
           arr[i] < arr[i + 1])
       {
           count++;
       }
    }
    return count;
}
 
// Driver Code
int main()
{
    int arr[] = { 3, 2, 5 };
    int n = sizeof(arr) / sizeof(arr[0]);
     
    cout << countValleys(n, arr);
}
 
// This code is contributed by Surendra_Gangwar

// Java program to count the number
// of valley points in the array
 
import java.io.*;
 
class GFG {
 
    // Function to count the valley points
    // in the given character array
    static int countValleys(int n, int arr[])
    {
        int count = 0, temp = 0;
 
        // Loop to iterate over the elements
        // of the given array
        for (int i = 1; i < n - 1; i++) {
 
            // Condition to check if the given
            // element is a valley point
            if (arr[i - 1] > arr[i]
                && arr[i] < arr[i + 1]) {
                count++;
            }
        }
        return count;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
        int arr[] = { 3, 2, 5 };
        int n = arr.length;
        System.out.println(
            countValleys(n, arr));
    }
}

# Python3 program to count the number
# of valley points in the array
 
# Function to count the valley points
# in the given character array
def countValleys(n, arr):
 
    count = 0; temp = 0;
 
    # Loop to iterate over the
    # elements of the given array
    for i in range(1, n):
 
        # Condition to check if the given
        # element is a valley point
        if (arr[i - 1] > arr[i] and
            arr[i] < arr[i + 1]):
 
            count += 1;
 
    return count;
 
# Driver Code
arr = [ 3, 2, 5 ];
n = len(arr);
     
print(countValleys(n, arr));
 
# This code is contributed by Code_Mech

// C# program to count the number
// of valley points in the array
using System;
class GFG{
 
// Function to count the valley points
// in the given character array
static int countValleys(int n, int []arr)
{
    int count = 0;
 
    // Loop to iterate over the elements
    // of the given array
    for (int i = 1; i < n - 1; i++)
    {
 
        // Condition to check if the given
        // element is a valley point
        if (arr[i - 1] > arr[i] &&
            arr[i] < arr[i + 1])
        {
            count++;
        }
    }
    return count;
}
 
// Driver Code
public static void Main()
{
    int []arr = { 3, 2, 5 };
    int n = arr.Length;
    Console.Write(countValleys(n, arr));
}
}
 
// This code is contributed by Code_Mech

<script>
 
// Javascript program to count the number
// of valley points in the array
 
// Function to count the valley points
// in the given character array
function countValleys(n, arr)
{
    let count = 0, temp = 0;
     
    // Loop to iterate over the
    // elements of the given array
    for(let i = 1; i < n - 1; i++)
    {
        
       // Condition to check if the given
       // element is a valley point
       if (arr[i - 1] > arr[i] &&
           arr[i] < arr[i + 1])
       {
           count++;
       }
    }
    return count;
}
 
// Driver Code
let arr = [ 3, 2, 5 ];
let n = arr.length;
 
document.write(countValleys(n, arr));
 
// This code is contributed by rishavmahato348
 
</script>

1

Complejidad de tiempo: O(n)

Espacio Auxiliar: O(1)