3Sum Closest LeetCode solution in Rust

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impl Solution {
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  pub fn three_sum_closest(mut nums: Vec<i32>, target: i32) -> i32 {
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    // [1] sorting would allow us to use two pointers
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    nums.sort_unstable();
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    let mut best_diff: i32 = i32::MAX;
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    // [2] use two pointers 'l' and 'r' that converge towards
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    //     one another for each first element 'i'
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    for i in 0..nums.len() {
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      let mut l = i + 1;
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      let mut r = nums.len() - 1;
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      let pre_diff = nums[i] - target;
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      while l < r {
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        let diff = pre_diff + nums[l] + nums[r];
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        if diff.abs() < best_diff.abs() {
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          best_diff = diff;
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        }
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        match diff.signum() {
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          1 => r -= 1,
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          -1 => l += 1,
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          0 => return target,
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          _ => unreachable!(),
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        }
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      }
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    }
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    return target + best_diff;
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  }
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}