<p>You are given a string s of length <code>n</code> containing only four kinds of characters: <code>&#39;Q&#39;</code>, <code>&#39;W&#39;</code>, <code>&#39;E&#39;</code>, and <code>&#39;R&#39;</code>.</p>

<p>A string is said to be <strong>balanced</strong><em> </em>if each of its characters appears <code>n / 4</code> times where <code>n</code> is the length of the string.</p>

<p>Return <em>the minimum length of the substring that can be replaced with <strong>any</strong> other string of the same length to make </em><code>s</code><em> <strong>balanced</strong></em>. If s is already <strong>balanced</strong>, return <code>0</code>.</p>

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

<pre>
<strong>Input:</strong> s = &quot;QWER&quot;
<strong>Output:</strong> 0
<strong>Explanation:</strong> s is already balanced.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;QQWE&quot;
<strong>Output:</strong> 1
<strong>Explanation:</strong> We need to replace a &#39;Q&#39; to &#39;R&#39;, so that &quot;RQWE&quot; (or &quot;QRWE&quot;) is balanced.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;QQQW&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> We can replace the first &quot;QQ&quot; to &quot;ER&quot;. 
</pre>

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

<ul>
	<li><code>n == s.length</code></li>
	<li><code>4 &lt;= n &lt;= 10<sup>5</sup></code></li>
	<li><code>n</code> is a multiple of <code>4</code>.</li>
	<li><code>s</code> contains only <code>&#39;Q&#39;</code>, <code>&#39;W&#39;</code>, <code>&#39;E&#39;</code>, and <code>&#39;R&#39;</code>.</li>
</ul>

class Solution:
    
    def balancedString(self, s: str) -> int:
            n = len(s); avg = n//4
            std = '';
            dic = {'Q':0, 'W':0, 'E':0, 'R':0}
            for c in s:
                dic[c] += 1
            for c, v in dic.items():
                if v > avg:
                    std += c * (v-avg)
            print(std)
            if not std: return 0
            return self.minWindow(s, std)
        
    def minWindow(self, s: str, t: str) -> str:
            # sliding window: Time: O(s+t); Space: O(s+t)
            l = r = formed = 0  # keep track of how many unique characters in t are present in the current window in its desired frequency
            tdic = Counter(t)
            window = {}
            ans = (float('inf'), None, None)  # tuple: (win_length, left, right)

            while r < len(s):
                window[s[r]] = window.get(s[r], 0) + 1
                if s[r] in tdic and window[s[r]] == tdic[s[r]]:
                    formed += 1
                while l <= r and formed == len(tdic):  
                    if r - l + 1 < ans[0]:  # update window length to maintain minimum
                        ans = (r-l+1, l, r)
                    window[s[l]] -= 1
                    if s[l] in tdic and window[s[l]] < tdic[s[l]]:
                        formed -= 1
                    l += 1
                r += 1
            return 0 if ans[0] == float('inf') else len(s[ans[1]:ans[2]+1])
123