1705. Maximum Number of Eaten Apples

There is a special kind of apple tree that grows apples every day for n days. On the ith day, the tree grows apples[i] apples that will rot after days[i] days, that is on day i + days[i] the apples will be rotten and cannot be eaten. On some days, the apple tree does not grow any apples, which are denoted by apples[i] == 0 and days[i] == 0.

You decided to eat at most one apple a day (to keep the doctors away). Note that you can keep eating after the first n days.

Given two integer arrays days and apples of length n, return the maximum number of apples you can eat.

 

Example 1:

Input: apples = [1,2,3,5,2], days = [3,2,1,4,2]
Output: 7
Explanation: You can eat 7 apples:
- On the first day, you eat an apple that grew on the first day.
- On the second day, you eat an apple that grew on the second day.
- On the third day, you eat an apple that grew on the second day. After this day, the apples that grew on the third day rot.
- On the fourth to the seventh days, you eat apples that grew on the fourth day.

Example 2:

Input: apples = [3,0,0,0,0,2], days = [3,0,0,0,0,2]
Output: 5
Explanation: You can eat 5 apples:
- On the first to the third day you eat apples that grew on the first day.
- Do nothing on the fouth and fifth days.
- On the sixth and seventh days you eat apples that grew on the sixth day.

 

Constraints:

  • apples.length == n
  • days.length == n
  • 1 <= n <= 2 * 104
  • 0 <= apples[i], days[i] <= 2 * 104
  • days[i] = 0 if and only if apples[i] = 0.

Rust Solution

struct Solution;
use std::cmp::Reverse;
use std::collections::BinaryHeap;

impl Solution {
    fn eaten_apples(apples: Vec<i32>, days: Vec<i32>) -> i32 {
        let n = apples.len();
        let mut queue: BinaryHeap<Reverse<(usize, i32)>> = BinaryHeap::new();
        let mut i = 0;
        let mut res = 0;
        loop {
            if i < n {
                queue.push(Reverse((i + days[i] as usize, apples[i])));
            }
            if i >= n && queue.is_empty() {
                break;
            }
            while let Some(Reverse((j, left))) = queue.peek() {
                if i >= *j || *left == 0 {
                    queue.pop();
                } else {
                    break;
                }
            }
            if let Some(mut top) = queue.peek_mut() {
                (top.0).1 -= 1;
                res += 1;
            }
            i += 1;
        }
        res
    }
}

#[test]
fn test() {
    let apples = vec![1, 2, 3, 5, 2];
    let days = vec![3, 2, 1, 4, 2];
    let res = 7;
    assert_eq!(Solution::eaten_apples(apples, days), res);
    let apples = vec![3, 0, 0, 0, 0, 2];
    let days = vec![3, 0, 0, 0, 0, 2];
    let res = 5;
    assert_eq!(Solution::eaten_apples(apples, days), res);
}

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