Find Latest Group of Size M LeetCode solution in C++

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class Solution {
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 public:
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  int findLatestStep(vector<int> &arr, int m) {
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    int n = size(arr), ans = -1;
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    vector<int> cntL(n + 2), indL(n + 2);
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    for (int i = 0; i < n; i++) {
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      int li = indL[arr[i] - 1], ri = indL[arr[i] + 1], nl = li + ri + 1;
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      indL[arr[i]] = nl;
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      indL[arr[i] - li] = nl;
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      indL[arr[i] + ri] = nl;
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      cntL[li]--;
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      cntL[ri]--;
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      cntL[nl]++;
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      if (cntL[m] > 0) ans = i + 1;
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    }
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    return ans;
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  }
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};