# Longest Mountain in Array in C++

C++Server Side ProgrammingProgramming

Consider any (contiguous) subarray B (of A) a called mountain if the following properties hold −

• size of B >= 3
• There exists some 0 < i < B.length - 1 such that B[0] < B[1] < ... B[i-1] < B[i] > B[i+1] > ... > B[B.length - 1]

Suppose we have an array A of integers; we have to find the length of the longest mountain. We have to return 0 if there is no mountain. So if the input is like [2,1,4,7,3,2,5], then the result will be 5. So the largest mountain will be [1,4,7,3,2], whose length is 5.

To solve this, we will follow these steps −

• ret := 0, n := size of array a
• i := 0 to n – 1, increase i by j + 1
• j := i
• down := false, up := false
• while j + 1 < n and a[j + 1] > a[j]
• up := true and increase j by 1
• while up is true and j + 1 < n and a[j + 1] > a[j]
• down := true and increase j by 1
• if up and down both are true, set ret := max of j – i + 1 and ret, decrease j by 1
• return ret.

Let us see the following implementation to get better understanding −

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int longestMountain(vector<int>& a) {
int ret = 0;
int n = a.size();
int j;
for(int i = 0; i < n; i = j + 1){
j = i;
bool down = false;
bool up = false;
while(j + 1 < n && a[j + 1] > a[j]) {
up = true;
j++;
}
while(up && j + 1 < n && a[j + 1] < a[j]){
down = true;
j++;
}
if(up && down){
ret = max(j - i + 1, ret);
j--;
}
}
return ret;
}
};
main(){
vector<int> v = {2,1,4,7,3,2,5};
Solution ob;
cout << (ob.longestMountain(v));
}

## Input

[2,1,4,7,3,2,5]

## Output

5
Published on 05-May-2020 10:20:39