Minimum Index of a Valid Split
<p>An element <code>x</code> of an integer array <code>arr</code> of length <code>m</code> is <strong>dominant</strong> if <strong>more than half</strong> the elements of <code>arr</code> have a value of <code>x</code>.</p>

<p>You are given a <strong>0-indexed</strong> integer array <code>nums</code> of length <code>n</code> with one <strong>dominant</strong> element.</p>

<p>You can split <code>nums</code> at an index <code>i</code> into two arrays <code>nums[0, ..., i]</code> and <code>nums[i + 1, ..., n - 1]</code>, but the split is only <strong>valid</strong> if:</p>

<ul>
	<li><code>0 &lt;= i &lt; n - 1</code></li>
	<li><code>nums[0, ..., i]</code>, and <code>nums[i + 1, ..., n - 1]</code> have the same dominant element.</li>
</ul>

<p>Here, <code>nums[i, ..., j]</code> denotes the subarray of <code>nums</code> starting at index <code>i</code> and ending at index <code>j</code>, both ends being inclusive. Particularly, if <code>j &lt; i</code> then <code>nums[i, ..., j]</code> denotes an empty subarray.</p>

<p>Return <em>the <strong>minimum</strong> index of a <strong>valid split</strong></em>. If no valid split exists, return <code>-1</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,2,2]
<strong>Output:</strong> 2
<strong>Explanation:</strong> We can split the array at index 2 to obtain arrays [1,2,2] and [2]. 
In array [1,2,2], element 2 is dominant since it occurs twice in the array and 2 * 2 &gt; 3. 
In array [2], element 2 is dominant since it occurs once in the array and 1 * 2 &gt; 1.
Both [1,2,2] and [2] have the same dominant element as nums, so this is a valid split. 
It can be shown that index 2 is the minimum index of a valid split. </pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [2,1,3,1,1,1,7,1,2,1]
<strong>Output:</strong> 4
<strong>Explanation:</strong> We can split the array at index 4 to obtain arrays [2,1,3,1,1] and [1,7,1,2,1].
In array [2,1,3,1,1], element 1 is dominant since it occurs thrice in the array and 3 * 2 &gt; 5.
In array [1,7,1,2,1], element 1 is dominant since it occurs thrice in the array and 3 * 2 &gt; 5.
Both [2,1,3,1,1] and [1,7,1,2,1] have the same dominant element as nums, so this is a valid split.
It can be shown that index 4 is the minimum index of a valid split.</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [3,3,3,3,7,2,2]
<strong>Output:</strong> -1
<strong>Explanation:</strong> It can be shown that there is no valid split.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
	<li><code>nums</code> has exactly one dominant element.</li>
</ul>
Array; Hash Table; Sorting
class Solution {
    public int minimumIndex(List<Integer> nums) {
        int x = 0, cnt = 0;
        Map<Integer, Integer> freq = new HashMap<>();
        for (int v : nums) {
            int t = freq.merge(v, 1, Integer::sum);
            if (cnt < t) {
                cnt = t;
                x = v;
            }
        }
        int cur = 0;
        for (int i = 1; i <= nums.size(); ++i) {
            if (nums.get(i - 1) == x) {
                ++cur;
                if (cur * 2 > i && (cnt - cur) * 2 > nums.size() - i) {
                    return i - 1;
                }
            }
        }
        return -1;
    }
}