Find the Middle Index in Array LeetCode solution in C++

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class Solution {
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 public:
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  int findMiddleIndex(vector<int> &nums) {
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    int n = nums.size();
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    int left_sum = 0;
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    int right_sum = 0;
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    for (int i = 0; i < n; i++) {
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      right_sum += nums[i];
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    }
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    for (int i = 0; i < n; i++) {
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      right_sum -= nums[i];
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      if (left_sum == right_sum) {
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        return i;
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      }
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      left_sum += nums[i];
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    }
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    return -1;
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  }
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};