本蒟蒻写了一个双指针算法，只得了 $50$ 分。求助

#include <bits/stdc++.h>
using namespace std;

int a[55][1000010];

struct node {
    int x, color;
    bool operator < (const node &cmp2) const {
        return x < cmp2.x;
    }
};

int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i ++) {
        scanf ("%d", &a[i][0]);
        for (int j = 1; j <= a[i][0]; j ++)
            scanf ("%d", &a[i][j]);
    }
    vector <node> b;
    for (int i = 1; i <= n; i ++)
        for (int j = 1; j <= a[i][0]; j ++)
            b.push_back({a[i][j], i});
    sort (b.begin(), b.end());
    int len = b.size();
    int l = 1, r = 1;
    while (r <= len && l <= len) {
        r = l;
        int tri = 3;
        bool flag = false;
        vector <node> c;
        map <int, bool> vis, vis2;
        while (tri --) {
            while (r <= len && vis[b[r].color])
                r ++;
            if (r > len) {
                puts("NIE");
                return 0;
            }
            c.push_back(b[r]);
            vis[b[r].color] = true;
            r ++;
        }
        if (c[0].x + c[1].x > c[2].x) {
            cout << c[0].color << ' ' << c[0].x << ' ' << c[1].color <<
                 ' ' << c[1].x << ' ' << c[2].color << ' ' << c[2].x;
            return 0;
        }
        l = r;
    }
    puts("NIE");
    return 0;
}