最长单调上升子序列问题

请问下面两段代码的区别是什么

#include 
using namespace std;

const int N = 1e5 + 5;
int a[N], x, n,m;
int g[N], cnt;

int main() {
	cin>>m;
    while (m--) 
	{
		cin>>x;
		a[++n] = x;
	}
   
    cnt = 0;
    g[0] = -2e9;
    for (int i = 1; i <= n; i++) {
        if (a[i] > g[cnt]) g[++cnt] = a[i];
        else {
            int l = 1, r = cnt;
            while (l < r) {
                int mid = l + r >> 1;
                if (g[mid] >=a[i]) r = mid;
                else l = mid + 1;
            }
            g[l] = a[i];
        }
    }
    cout << cnt << endl;   // 最长上升子序列
}

#include 
using namespace std;

const int N = 1e5 + 5;
int a[N], x, n,m;
int g[N], cnt;

int main() {
	cin>>m;
    while (m--) 
	{
		cin>>x;
		a[++n] = x;
	}
   
    cnt = 0;
    g[0] = -2e9;
    for (int i = 1; i <= n; i++) {
        if (a[i] > g[cnt]) g[++cnt] = a[i];
        else {
            int l = 1, r = cnt;
            while (l < r) {
                int mid = l + r >> 1;
                if (g[mid] >a[i]) r = mid;
                else l = mid + 1;
            }
            g[l] = a[i];
        }
    }
    cout << cnt << endl;   // 最长上升子序列
}

为什么在求最长公共子序列时，f[mid]大于等于或大于a[i]都可以，而在最长单调上升子序列中只能大于等于，不能大于