<p>Given an array of integers&nbsp;<code>arr</code>, replace each element with its rank.</p>

<p>The rank represents how large the element is. The rank has the following rules:</p>

<ul>
	<li>Rank is an integer starting from 1.</li>
	<li>The larger the element, the larger the rank. If two elements are equal, their rank must be the same.</li>
	<li>Rank should be as small as possible.</li>
</ul>

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

<pre>
<strong>Input:</strong> arr = [40,10,20,30]
<strong>Output:</strong> [4,1,2,3]
<strong>Explanation</strong>: 40 is the largest element. 10 is the smallest. 20 is the second smallest. 30 is the third smallest.</pre>

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

<pre>
<strong>Input:</strong> arr = [100,100,100]
<strong>Output:</strong> [1,1,1]
<strong>Explanation</strong>: Same elements share the same rank.
</pre>

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

<pre>
<strong>Input:</strong> arr = [37,12,28,9,100,56,80,5,12]
<strong>Output:</strong> [5,3,4,2,8,6,7,1,3]
</pre>

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

<ul>
	<li><code>0 &lt;= arr.length &lt;= 10<sup>5</sup></code></li>
	<li><code>-10<sup>9</sup>&nbsp;&lt;= arr[i] &lt;= 10<sup>9</sup></code></li>
</ul>

#include <algorithm>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using std::unordered_map;
using std::unordered_set;
using std::vector;
class Solution {
public:
  vector<int> arrayRankTransform(vector<int> &arr) {
    unordered_set<int> tmpSet(arr.begin(), arr.end());
    vector<int> tmp(tmpSet.begin(), tmpSet.end());

    std::sort(tmp.begin(), tmp.end());

    unordered_map<int, int> rankMap;
    for (int i = 0; i < tmp.size(); i++) {
      rankMap[tmp[i]] = i + 1;
    }

    std::transform(arr.begin(), arr.end(), arr.begin(),
                   [&](int x) { return rankMap[x]; });

    return arr;
  }
};
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