#include <bits/stdc++.h>
#define ll long long

using namespace std;
void fast(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    #ifndef ONLINE_JUDGE
      freopen("input.txt", "r", stdin);
      freopen("output.txt", "w", stdout);
    #endif
}

int calcLen(const vector<int>& a) {
    int n = a.size();
    int cur = 1, mx = 1;
    for (int i = 1; i < n; i++) {
        if (a[i] >= a[i-1]) {
            cur++;
            mx = max(mx, cur);
        } else {
            cur = 1;
        }
    }
    return mx;
}

// find the longest subsequence with one substitution allowed
int solve(const vector<int>& a) {
    int n = a.size();
    int res = 1;

    res = max(res, calcLen(a));

    unordered_map<int, vector<int>> pos;
    for (int i = 0; i < n; i++) {
        pos[a[i]].push_back(i);
    }

    for (const auto& p : pos) {
        int x = p.first;
        const vector<int>& inds = p.second;

        for (const auto& q : pos) {
            int y = q.first;

            if (y == x) continue;

            vector<int> b = a;
            for (int idx : inds) {
                b[idx] = y;
            }

            res = max(res, calcLen(b));
        }
    }

    return res;
}

int main() {
    vector<int> arr = {1, 7, 7, 2, 3, 7, 6, -20};
    cout  << solve(arr) << endl;
    return 0;
}

C++ Online Compiler

Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}