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impl Solution {
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  pub fn unique_paths(m: i32, n: i32) -> i32 {
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    let mut ans: i64 = 1;
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    for i in 1..=m as i64 - 1 {
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      ans = ans * (n as i64 - 1 + i) / i;
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    }
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    ans as i32
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  }
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}