Initialize an array length of size n+2 to track the length of the group at each position (with sentinels at both ends).
Use a counter to track how many groups of size m exist at each step.
For each step, set the bit at arr[i] to 1:
- Check the length of the group to the left and right.
- The new group size is left + right + 1.
- Update the length array at the boundaries.
- Update the counter for groups of size m (decrement for old groups, increment for new group if size matches m).
If at any step the counter is positive, record the step as the latest.
Return the latest step found, or -1 if none.

Code

[{"language":"C++","code":"class Solution {\npublic:\n    int findLatestStep(vector<int>& arr, int m) {\n        int n = arr.size(), res = -1, cnt = 0;\n        vector<int> length(n+2);\n        vector<int> count(n+1);\n        for (int i = 0; i < n; ++i) {\n            int pos = arr[i];\n            int left = length[pos-1], right = length[pos+1];\n            int total = left + right + 1;\n            length[pos-left] = length[pos+right] = total;\n            if (left > 0) count[left]--;\n            if (right > 0) count[right]--;\n            count[total]++;\n            if (count[m] > 0) res = i+1;\n        }\n        return res;\n    }\n};","lang":"cpp","html":"<pre class=\"shiki shiki-themes github-light github-dark\" style=\"background-color:#fff;--shiki-dark-bg:#24292e;color:#24292e;--shiki-dark:#e1e4e8\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">class</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> Solution</span><span style=\"color:#24292E;--shiki-dark:#E1E4E8\"> {</span></span>\n<span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">public:</span></span>\n<span class=\"line\"><span style=\"colo

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