I am aware that there are many algorithms for finding longest increasing subsequence, but the algorithms using DP all have this is common - they recurse/ dynimacally calculate longest subsequence "ENDING" at a particular element of the array.
I wrote a solution which resurses taking longest subsequence "starting" at a particular array, which seems to work fine too.
#include<iostream>
using namespace std;
#define boostio ios_base::sync_with_stdio(0);
int n;
int a[100000];
int t[100000] = {-1};
int lis(int i){
    if(t[i]!= -1){
        return t[i];
    }   
    if(i == n){t[i] = 1; return 1;
    }
    for (int x = i+1; x <= n ; ++x)
    {
        if(a[x] > a[i] and 1 + lis(x) > t[i]){
            t[i] = 1 + lis(x);
            //return t[i];
        }
    }
    if(t[i] != -1){
            return t[i];
        }
    t[i] = 1; return 1;
}
int main(){
    boostio;
    cin >> n;
    for (int i = 1; i <= n; ++i)
    {
        cin >> a[i];
    }
    fill(t, t + n+2 ,-1);
    Int m = 0;
    for (int i = 1; i <= n; ++i)
    {
        //cout << i << " " << lis(i) << endl;
        if(lis(i) >m) m= lis(i);
    }
    cout << m;
    return 0;
}
I am wondering, is this in any way worse than if we recurse on "last element" of subsequence instead of the first. They both appear to be order n square algorithms to me, so why isnt this algorithm more circulated. To me it seems more intuitive. Am I missing something?
