Find the Minimum and Maximum Number of Nodes Between Critical Points LeetCode solution in Java

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class Solution {
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  public int[] nodesBetweenCriticalPoints(ListNode head) {
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    int res[] = new int[] {-1, -1};
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    if (head == null || head.next == null || head.next.next == null) return res;
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    int minidx = Integer.MAX_VALUE, curridx = -1, lastidx = -1;
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    ListNode prev = head, ptr = head.next;
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    int idx = 1, minD = Integer.MAX_VALUE;
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    while (ptr != null && ptr.next != null) {
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      if ((ptr.val > prev.val && ptr.val > ptr.next.val)
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          || (ptr.val < prev.val && ptr.val < ptr.next.val)) {
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        if (idx < minidx) minidx = idx;
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        lastidx = curridx;
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        curridx = idx;
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        if (lastidx != -1 && curridx - lastidx < minD) minD = curridx - lastidx;
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      }
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      prev = ptr;
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      ptr = ptr.next;
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      idx++;
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    }
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    if (lastidx == -1) return res;
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    else {
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      res[0] = minD;
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      res[1] = curridx - minidx;
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    }
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    return res;
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  }
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}