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class Solution {
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  public int[] smallestRange(List<List<Integer>> nums) {
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    int[] res = {-100000, 100000};
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    PriorityQueue<int[]> pq = new PriorityQueue<>((a, b) -> a[0] - b[0]);
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    int max = Integer.MIN_VALUE;
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    int k = nums.size();
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    for (int i = 0; i < k; i++) {
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      int minElem = nums.get(i).get(0);
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      int[] arr = {minElem, 0, i};
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      max = Math.max(max, minElem);
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      pq.add(arr);
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    }
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    while (true) {
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      int min[] = pq.poll();
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      if (res[1] - res[0] > max - min[0]) {
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        res[1] = max;
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        res[0] = min[0];
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      }
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      min[1]++;
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      List<Integer> cur = nums.get(min[2]);
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      if (min[1] == cur.size()) {
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        break;
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      } else {
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        min[0] = cur.get(min[1]);
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        max = Math.max(max, cur.get(min[1]));
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        pq.add(min);
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      }
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    }
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    return res;
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  }
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}