<p>We are given <code>hours</code>, a list of the number of hours worked per day for a given employee.</p>

<p>A day is considered to be a <em>tiring day</em> if and only if the number of hours worked is (strictly) greater than <code>8</code>.</p>

<p>A <em>well-performing interval</em> is an interval of days for which the number of tiring days is strictly larger than the number of non-tiring days.</p>

<p>Return the length of the longest well-performing interval.</p>

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

<pre>
<strong>Input:</strong> hours = [9,9,6,0,6,6,9]
<strong>Output:</strong> 3
<strong>Explanation: </strong>The longest well-performing interval is [9,9,6].
</pre>

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

<pre>
<strong>Input:</strong> hours = [6,6,6]
<strong>Output:</strong> 0
</pre>

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

<ul>
	<li><code>1 &lt;= hours.length &lt;= 10<sup>4</sup></code></li>
	<li><code>0 &lt;= hours[i] &lt;= 16</code></li>
</ul>

class Solution:
    
    def longestWPI(self, hours: List[int]) -> int:
        presum = [0]
        sums = 0
        
        for h in hours:
            if h > 8:
                sums += 1
            else:
                sums -= 1
            presum.append(sums)
            
        stack = []
        for i in range(len(presum)):
            while not stack or presum[stack[-1]] > presum[i]:
                stack.append(i)
                
        res = 0
        for j in range(len(presum)-1, -1, -1):
            while stack and presum[stack[-1]] < presum[j]:
                res = max(res, j-stack.pop())
                
        return res
        
#     def longestWPI(self, hours: List[int]) -> int:
#         presum = [0]
#         sums = 0
        
#         for h in hours:
#             if h > 8:
#                 sums += 1
#             else:
#                 sums -= 1
#             presum.append(sums)
            
#         stack = []
        
#         for i in range(len(presum)):
#             while not stack or presum[stack[-1]] > presum[i]:
#                 stack.append(i)
        
#         res = 0
#         for j in range(len(presum)-1, -1, -1):
#             while stack and presum[stack[-1]] < presum[j]:
#                 res = max(res, j-stack.pop())
                
#         return res

        
17500