Check whether the given array is perfect or not

01 Apr, 2021
There is an array contains some non-negative integers. Check whether the array is perfect or not. An array is called perfect if it is first strictly increasing, then constant and finally strictly decreasing. Any of the three parts can be empty.Examples:  
Input : arr[] = {1, 8, 8, 8, 3, 2}
Output : Yes
The array is perfect as it is first
increasing, then constant and finally
decreasing.

Input : arr[] = {1, 1, 2, 2, 1}
Output : No
The first part is not strictly increasing

Input : arr[] = {4, 4, 4, 4}
Output : Yes
 
The approach is to iterate the array from the left to the right and increase i (that is 1 initially) while the next element is strictly more than previous. then, iterate the array from the left to the right and increase i while the two adjacent elements are equal. Finally, iterate array from the left to the right and increase i while the next element is strictly less than previous. If we reach end with this process, we say that the array is perfect. 
C++
Java
Python3
C#
PHP
Javascript
// CPP program to check whether the given array// is perfect or not.#include <iostream>using namespace std; int checkUnimodal(int arr[], int n){    // Cover first strictly increasing part    int i = 1;    while (arr[i] > arr[i - 1] && i < n)        ++i;     // Cover middle equal part    while (arr[i] == arr[i - 1] && i < n)        ++i;     // Cover last decreasing part    while (arr[i] < arr[i - 1] && i < n)        ++i;     // Return true if we reached end.    return (i == n);} int main(){    int arr[] = { 1, 5, 5, 5, 4, 2 };    int n = sizeof(arr) / sizeof(arr[0]);    if (checkUnimodal(arr, n))        cout << "Yes" << endl;    else        cout << "No" << endl;}
// Java program to check whether the given array// is perfect or not.import java.util.*; class Node{     static boolean checkUnimodal(int arr[], int n){    // Cover first strictly increasing part    int i = 1;    while (i < n && arr[i] > arr[i - 1])        ++i;     // Cover middle equal part    while (i < n && arr[i] == arr[i - 1])        ++i;     // Cover last decreasing part    while (i < n &&arr[i] < arr[i - 1])        ++i;     // Return true if we reached end.    return (i == n);} // Driver codepublic static void main(String[] args){    int arr[] = { 1, 5, 5, 5, 4, 2 };    int n = arr.length;    if (checkUnimodal(arr, n))        System.out.println("Yes");    else        System.out.println("No");}} // This code is contributed by 29AjayKumar
# Python 3 program to check whether the# given array is perfect or not. def checkUnimodal(arr, n):         # Cover first strictly increasing part    i = 1    while (i < n and arr[i] > arr[i - 1]):        i += 1     # Cover middle equal part    while (i < n and arr[i] == arr[i - 1]):        i += 1     # Cover last decreasing part    while (i < n and arr[i] < arr[i - 1]):        i += 1     # Return true if we reached end.    return (i == n) # Driver Codeif __name__ == '__main__':    arr = [1, 5, 5, 5, 4, 2 ]    n = len(arr)    if (checkUnimodal(arr, n)):        print("Yes")    else:        print("No") # This code is contributed by# Surendra_Gangwar
// C# program to check whether the given array// is perfect or not.using System; class GFG{    static bool checkUnimodal(int []arr, int n){    // Cover first strictly increasing part    int i = 1;    while (i < n && arr[i] > arr[i - 1])        ++i;     // Cover middle equal part    while (i < n && arr[i] == arr[i - 1])        ++i;     // Cover last decreasing part    while (i < n &&arr[i] < arr[i - 1])        ++i;     // Return true if we reached end.    return (i == n);} // Driver codestatic public void Main (){    int []arr = { 1, 5, 5, 5, 4, 2 };    int n = arr.Length;    if (checkUnimodal(arr, n))        Console.Write("Yes");    else        Console.Write("No");}} // This code is contributed by ajit..
<?php// PHP program to check whether the// given array is perfect or not. function check($arr, $n){    // Cover first strictly increasing part    $i = 1;    while ($arr[$i] > $arr[$i - 1] && $i < $n)        ++$i;     // Cover middle equal part    while ($arr[$i] == $arr[$i - 1] && $i < $n)        ++$i;     // Cover last decreasing part    while ($arr[$i] < $arr[$i - 1] && $i < $n)        ++$i;     // Return true if we reached end    return ($i == $n);} // Driver Code$arr = array(1, 5, 5, 5, 4, 2);$n = sizeof($arr);if (check($arr, $n))    echo "Yes";else    echo "No";     // This code is contributed by Akanksha Rai?>
<script>    // Javascript program to check whether the given array    // is perfect or not.         function checkUnimodal(arr, n)    {        // Cover first strictly increasing part        let i = 1;        while (arr[i] > arr[i - 1] && i < n)            ++i;         // Cover middle equal part        while (arr[i] == arr[i - 1] && i < n)            ++i;         // Cover last decreasing part        while (arr[i] < arr[i - 1] && i < n)            ++i;         // Return true if we reached end.        return (i == n);    }         let arr = [ 1, 5, 5, 5, 4, 2 ];    let n = arr.length;    if (checkUnimodal(arr, n))        document.write("YES");    else        document.write("NO"); </script>
Output: 
YES
 
SURENDRA_GANGWAR
Akanksha_Rai
29AjayKumar
jit_t
suresh07
Arrays
Arrays
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Introduction to Data Structures
Window Sliding Technique
Search, insert and delete in an unsorted array
Chocolate Distribution Problem
Find duplicates in O(n) time and O(1) extra space | Set 1
What is Data Structure: Types, Classifications and Applications
Next Greater Element
Move all negative numbers to beginning and positive to end with constant extra space
Count pairs with given sum
Find subarray with given sum | Set 1 (Nonnegative Numbers)