45 lines
957 B
Rust
45 lines
957 B
Rust
#[derive(Debug)]
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struct NumArray {
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prefix_sums: Vec<i32>,
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}
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impl NumArray {
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fn new(nums: Vec<i32>) -> Self {
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let mut total = nums.iter().sum::<i32>();
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let mut prefix_sums: Vec<i32> = nums
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.iter()
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.scan(total, |total, &x| {
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let prev = *total;
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*total -= x;
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Some(prev)
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})
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.collect();
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prefix_sums.push(0);
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Self { prefix_sums }
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}
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fn sum_range(&self, left: i32, right: i32) -> i32 {
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self.prefix_sums[left as usize] - self.prefix_sums[right as usize + 1]
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}
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}
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fn main() {}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn example_1() {
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let num_arr = NumArray::new(vec![-2, 0, 3, -5, 2, -1]);
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dbg!("{:?}", &num_arr);
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assert_eq!(num_arr.sum_range(0, 2), 1);
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assert_eq!(num_arr.sum_range(2, 5), -1);
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assert_eq!(num_arr.sum_range(0, 5), -3);
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}
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}
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