为什么会ce，按道理应该可以拿一半分啊？

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

const int maxn = 100100;

int n, ans[maxn][maxn], a[maxn], b[maxn];

int max(int a, int b){
    return a > b ? a:b;
}

int main(){
    scanf("%d", &n);
    for (int i = 1; i <= n; ++i)
        scanf("%d", &a[i]);
    for (int i = 1; i <= n; ++i)
        scanf("%d", &b[i]);
    for (int i = 0; i <= n; ++i){
        for (int j = 0; j <= n; ++j){
            if ( i == 0 || j == 0){
                ans[i][j] = 0;
                continue;
            }
            if (a[i] == b[j])
                ans[i][j] = ans[i - 1][j - 1] + 1;
            else
                ans[i][j] = max(ans[i][j - 1], ans[i - 1][j]);
        }
    }
    printf("%d\n", ans[n][n]);
    return 0;
}