<p>You are playing a game that contains multiple characters, and each of the characters has <strong>two</strong> main properties: <strong>attack</strong> and <strong>defense</strong>. You are given a 2D integer array <code>properties</code> where <code>properties[i] = [attack<sub>i</sub>, defense<sub>i</sub>]</code> represents the properties of the <code>i<sup>th</sup></code> character in the game.</p>

<p>A character is said to be <strong>weak</strong> if any other character has <strong>both</strong> attack and defense levels <strong>strictly greater</strong> than this character&#39;s attack and defense levels. More formally, a character <code>i</code> is said to be <strong>weak</strong> if there exists another character <code>j</code> where <code>attack<sub>j</sub> &gt; attack<sub>i</sub></code> and <code>defense<sub>j</sub> &gt; defense<sub>i</sub></code>.</p>

<p>Return <em>the number of <strong>weak</strong> characters</em>.</p>

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

<pre>
<strong>Input:</strong> properties = [[5,5],[6,3],[3,6]]
<strong>Output:</strong> 0
<strong>Explanation:</strong> No character has strictly greater attack and defense than the other.
</pre>

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

<pre>
<strong>Input:</strong> properties = [[2,2],[3,3]]
<strong>Output:</strong> 1
<strong>Explanation:</strong> The first character is weak because the second character has a strictly greater attack and defense.
</pre>

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

<pre>
<strong>Input:</strong> properties = [[1,5],[10,4],[4,3]]
<strong>Output:</strong> 1
<strong>Explanation:</strong> The third character is weak because the second character has a strictly greater attack and defense.
</pre>

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

<ul>
	<li><code>2 &lt;= properties.length &lt;= 10<sup>5</sup></code></li>
	<li><code>properties[i].length == 2</code></li>
	<li><code>1 &lt;= attack<sub>i</sub>, defense<sub>i</sub> &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution:
    def numberOfWeakCharacters(self, nums: List[List[int]]) -> int:
        nums.sort(key=lambda l: [l[0], -l[1]])

        maxdef = 0
        weak = 0
        for i in range(len(nums) - 1, -1, -1):
            if nums[i][1] < maxdef:
                weak += 1
            else:
                maxdef = nums[i][1]
        
        return weak

        # Time: O(nlog(n))
        # Using sorted groups and a stack, iterating left to right.
        #
        # nums.sort(key=lambda l: [l[0], -l[1]])
        # groups = [[nums[0]]]
        # for i in range(1, len(nums)):
        #     if nums[i][0] == groups[-1][0][0]:
        #         groups[-1].append(nums[i])
        #     else:
        #         groups.append([nums[i]])

        # s = groups[0]
        # for i in range(1, len(groups)):
        #     top = groups[i][0]
        #     while s and top[1] > s[-1][1]:
        #         s.pop()
        #     for tup in groups[i]:
        #         s.append(tup)
        
        # return len(nums) - len(s)
1908