代码

#include <algorithm> 

using namespace std;

int query_kth(const int *a, int n_a, const int *b, int n_b, const int *c, int n_c, int k)
{
    static const int *num[] = {a, b, c}, n[] = {n_a, n_b, n_c}, N = 3;
    int i, j, l, m[N] = {}, s[N];
    for (; k; k -= l + 1)
    {
        l = (k - N + 1) / N;
        for (i = j = 0; i < 3; ++i)
        {
            if (l + m[i] < n[i])
                s[i] = num[i][l + m[i]];
            else
                s[i] = 2e9;
            if (s[j] > s[i])
                j = i;
        }
        m[j] += l + 1;
    }
    return s[j];
}

评测结果