Solution.java

class Solution {
    public int[] smallestRange(List<List<Integer>> nums) {
        int n = 0;
        for (var v : nums) {
            n += v.size();
        }
        int[][] t = new int[n][2];
        int k = nums.size();
        for (int i = 0, j = 0; i < k; ++i) {
            for (int x : nums.get(i)) {
                t[j++] = new int[] {x, i};
            }
        }
        Arrays.sort(t, (a, b) -> a[0] - b[0]);
        int j = 0;
        Map<Integer, Integer> cnt = new HashMap<>();
        int[] ans = new int[] {-1000000, 1000000};
        for (int[] e : t) {
            int b = e[0];
            int v = e[1];
            cnt.put(v, cnt.getOrDefault(v, 0) + 1);
            while (cnt.size() == k) {
                int a = t[j][0];
                int w = t[j][1];
                int x = b - a - (ans[1] - ans[0]);
                if (x < 0 || (x == 0 && a < ans[0])) {
                    ans[0] = a;
                    ans[1] = b;
                }
                cnt.put(w, cnt.get(w) - 1);
                if (cnt.get(w) == 0) {
                    cnt.remove(w);
                }
                ++j;
            }
        }
        return ans;
    }
}