Given an array arr[]. The task is to check whether it is a mountain array or not. A mountain array is an array of length at least 3 with elements strictly increasing from starting till an index i, and then strictly decreasing from index i to last index. More formally arr[0] < arr[1] < arr[i] >arr[i+1] > arr[i+2] > arr[N-1].
Examples
Input: arr[] = {4, 4, 3, 2, 1}
Output: falseInput: arr = {1, 2, 3, 4, 9, 8, 7, 6, 5}
Output: true
Approach: This problem can be solved by traversing the array in two parts. Follow the steps below to solve the given problem.
- First, traverse from start till the index where the current element becomes smaller than its immediate previous one.
- Then from this index, traverse till the last index and check if the current element is strictly smaller than the previous one.
- If both the conditions are true, return true.
- Else at any point, the condition fails, return false.
Below is the implementation of the above approach.
C++
// C++ program for above approach#include <bits/stdc++.h>using namespace std;// Function to check if the given array// is mountain array or notbool isMountainArray(vector<int>& arr){ if (arr.size() < 3) return false; int flag = 0, i = 0; for (i = 1; i < arr.size(); i++) if (arr[i] <= arr[i - 1]) break; if (i == arr.size() || i == 1) return false; for (; i < arr.size(); i++) if (arr[i] >= arr[i - 1]) break; return i == arr.size();}// Driver Codeint main(){ vector<int> arr = { 1, 2, 3, 4, 9, 8, 7, 6, 5 }; cout << (isMountainArray(arr) ? "true" : "false"); return 0;} |
Java
// Java program for the above approachimport java.io.*;import java.lang.*;import java.util.*;class GFG {// Function to check if the given array// is mountain array or notstatic Boolean isMountainArray(int arr[]){ if (arr.length < 3) return false; int flag = 0, i = 0; for (i = 1; i < arr.length; i++) if (arr[i] <= arr[i - 1]) break; if (i == arr.length || i == 1) return false; for (; i < arr.length; i++) if (arr[i] >= arr[i - 1]) break; return i == arr.length;}// Driver Code public static void main (String[] args) { int arr[] = { 1, 2, 3, 4, 9, 8, 7, 6, 5 }; System.out.println(isMountainArray(arr) ? "true" : "false"); }}// This code is contributed by hrithikgarg03188. |
Python3
# Python 3 program for above approach# Function to check if the given array# is mountain array or notdef isMountainArray(arr): if (len(arr) < 3): return False flag = 0 i = 0 for i in range(1, len(arr)): if (arr[i] <= arr[i - 1]): break if (i == len(arr) or i == 1): return False while i < len(arr): if (arr[i] >= arr[i - 1]): break i += 1 return i == len(arr)# Driver Codeif __name__ == "__main__": arr = [1, 2, 3, 4, 9, 8, 7, 6, 5] if (isMountainArray(arr)): print("true") else: print("false") # This code is contributed by ukasp. |
C#
// C# program for above approachusing System;class GFG{ // Function to check if the given array // is mountain array or not static bool isMountainArray(int[] arr) { if (arr.Length < 3) return false; int i = 0; for (i = 1; i < arr.Length; i++) if (arr[i] <= arr[i - 1]) break; if (i == arr.Length || i == 1) return false; for (; i < arr.Length; i++) if (arr[i] >= arr[i - 1]) break; return i == arr.Length; } // Driver Code public static int Main() { int[] arr = { 1, 2, 3, 4, 9, 8, 7, 6, 5 }; Console.Write(isMountainArray(arr) ? "true" : "false"); return 0; }}// This code is contributed by Taranpreet |
Javascript
<script> // JavaScript program for above approach // Function to check if the given array // is mountain array or not const isMountainArray = (arr) => { if (arr.length < 3) return false; let flag = 0, i = 0; for (i = 1; i < arr.length; i++) if (arr[i] <= arr[i - 1]) break; if (i == arr.length || i == 1) return false; for (; i < arr.length; i++) if (arr[i] >= arr[i - 1]) break; return i == arr.length; } // Driver Code let arr = [1, 2, 3, 4, 9, 8, 7, 6, 5]; (isMountainArray(arr) ? document.write("true") : document.write("false"));// This code is contributed by rakeshsahni</script> |
Output
true
Time Complexity: O(N)
Auxiliary Space: O(1)
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