Maximum Number of Groups Entering a Competition LeetCode solution in Rust

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/// @author: Leon
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/// https://leetcode.com/problems/maximum-number-of-groups-entering-a-competition/
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/// Time Complexity:    O(`len_gs`)
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/// Space Complexity:   O(1)
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impl Solution {
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  pub fn maximum_groups(grades: Vec<i32>) -> i32 {
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    let len_gs: i32 = grades.len() as i32;
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    let mut cnt: i32 = 0;
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    // the running length of the (current) subarray
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    let mut len: i32 = 1;
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    // the accumulated sum of lengths (of subarrays)
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    let mut sum: i32 = 0;
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    while sum + len <= len_gs {
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      cnt += 1;
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      sum += len;
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      len += 1;
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    }
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    cnt
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  }
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}