<p>You are given a binary string <code>s</code>. In one second, <strong>all</strong> occurrences of <code>&quot;01&quot;</code> are <strong>simultaneously</strong> replaced with <code>&quot;10&quot;</code>. This process <strong>repeats</strong> until no occurrences of <code>&quot;01&quot;</code> exist.</p>

<p>Return<em> the number of seconds needed to complete this process.</em></p>

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

<pre>
<strong>Input:</strong> s = &quot;0110101&quot;
<strong>Output:</strong> 4
<strong>Explanation:</strong> 
After one second, s becomes &quot;1011010&quot;.
After another second, s becomes &quot;1101100&quot;.
After the third second, s becomes &quot;1110100&quot;.
After the fourth second, s becomes &quot;1111000&quot;.
No occurrence of &quot;01&quot; exists any longer, and the process needed 4 seconds to complete,
so we return 4.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;11100&quot;
<strong>Output:</strong> 0
<strong>Explanation:</strong>
No occurrence of &quot;01&quot; exists in s, and the processes needed 0 seconds to complete,
so we return 0.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
	<li><code>s[i]</code> is either <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>
</ul>

<p>&nbsp;</p>
<p><strong>Follow up:</strong></p>

<p>Can you solve this problem in O(n) time complexity?</p>

def test(s):
    zero = False
    for ch in s:
        if ch=='1' and zero:
            return False
        if ch=='0':
            zero = True
    return True

class Solution:
    def secondsToRemoveOccurrences(self, s: str) -> int:
        c = 0
        while not test(s):
            c += 1
            s = s.replace('01', "a")
            s = s.replace('a', "10")
        return c

        # trying to be smart... but doesn't work :/
        prev = '0'
        prev_c = 0
        maxi = 0
        i = 0
        for ch in s[::-1]:
            print(ch)
            if ch=='0':
                print(' ', i+prev_c)
                maxi = max(maxi, i + prev_c)
                if i>0 and prev=='0':
                    prev_c += 1
                prev = '0'
            else:
                i += 1
                prev = '1'
        return maxi
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