<p>You are given a string <code>s</code> of lowercase English letters and a 2D integer array <code>shifts</code> where <code>shifts[i] = [start<sub>i</sub>, end<sub>i</sub>, direction<sub>i</sub>]</code>. For every <code>i</code>, <strong>shift</strong> the characters in <code>s</code> from the index <code>start<sub>i</sub></code> to the index <code>end<sub>i</sub></code> (<strong>inclusive</strong>) forward if <code>direction<sub>i</sub> = 1</code>, or shift the characters backward if <code>direction<sub>i</sub> = 0</code>.</p>

<p>Shifting a character <strong>forward</strong> means replacing it with the <strong>next</strong> letter in the alphabet (wrapping around so that <code>&#39;z&#39;</code> becomes <code>&#39;a&#39;</code>). Similarly, shifting a character <strong>backward</strong> means replacing it with the <strong>previous</strong> letter in the alphabet (wrapping around so that <code>&#39;a&#39;</code> becomes <code>&#39;z&#39;</code>).</p>

<p>Return <em>the final string after all such shifts to </em><code>s</code><em> are applied</em>.</p>

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

<pre>
<strong>Input:</strong> s = &quot;abc&quot;, shifts = [[0,1,0],[1,2,1],[0,2,1]]
<strong>Output:</strong> &quot;ace&quot;
<strong>Explanation:</strong> Firstly, shift the characters from index 0 to index 1 backward. Now s = &quot;zac&quot;.
Secondly, shift the characters from index 1 to index 2 forward. Now s = &quot;zbd&quot;.
Finally, shift the characters from index 0 to index 2 forward. Now s = &quot;ace&quot;.</pre>

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

<pre>
<strong>Input:</strong> s = &quot;dztz&quot;, shifts = [[0,0,0],[1,1,1]]
<strong>Output:</strong> &quot;catz&quot;
<strong>Explanation:</strong> Firstly, shift the characters from index 0 to index 0 backward. Now s = &quot;cztz&quot;.
Finally, shift the characters from index 1 to index 1 forward. Now s = &quot;catz&quot;.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length, shifts.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>shifts[i].length == 3</code></li>
	<li><code>0 &lt;= start<sub>i</sub> &lt;= end<sub>i</sub> &lt; s.length</code></li>
	<li><code>0 &lt;= direction<sub>i</sub> &lt;= 1</code></li>
	<li><code>s</code> consists of lowercase English letters.</li>
</ul>

class Solution:
    def shiftingLetters(self, s: str, shifts: List[List[int]]) -> str:
        memory = []
        acc = [0] * (len(s) + 1)
        for start, end, direction in shifts:
            parity = 1 if direction else -1
            memory.append((start, parity))
            memory.append((end + 1, -parity))

        memory.sort()
        for index, value in memory:
            acc[index] += value
        acc = [num % 26 for num in accumulate(acc)]


        ans = []
        for index, letter in enumerate(s):
            result = (acc[index] + (ord(letter) - ord('a'))) % 26
            ans.append(chr(result + ord('a')))
        return ''.join(ans)

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