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class Solution {
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  public ListNode deleteDuplicates(ListNode head) {
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    if (head == null) return head;
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    ListNode temp = head;
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    int last = -1;
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    int[] array = new int[201];
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    // zero == index 100
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    // one == index 101;
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    // -100 == index 0;
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    while (temp != null) {
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      array[temp.val + 100]++;
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      temp = temp.next;
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    }
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    for (int i = 0; i < 201; i++) {
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      if (array[i] == 1) {
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        last = i;
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      }
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    }
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    if (last == -1) return null;
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    temp = head;
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    for (int i = 0; i < 201; i++) {
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      if (array[i] == 1) {
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        temp.val = i - 100;
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        if (i == last) {
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          temp.next = null;
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          break;
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        }
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        temp = temp.next;
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      }
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    }
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    temp.next = null;
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    return head;
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  }
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}