LeetCode Entry
2779. Maximum Beauty of an Array After Applying Operation
Max equal nums after adjusting to [-k..+k] search sweep
2779. Maximum Beauty of an Array After Applying Operation medium
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Problem TLDR
Max equal nums after adjusting to [-k..+k] #medium #binary_search #line_sweep
Intuition
Let’s observe the data:
// 4 6 1 2 k=2
// 2 4-1 0
// 3 5 0 1
// 4 6 1 2
// 5 7 2 3
// 6 8 3 4
//[2..6] [6..8] [-1..3] [0..4]
// -1 0 1 2 3 4 5 6 7 8
// s * e
// s * * e
// s * e
// s e
// 1 2 3 3 2 2 1
// -16 17 42 75 100
// [ ]
// [ ]
// [ ]
// s s e e e
// s
We can notice, each number is actually an interval of [n-k..n+k]. The task is to find maximum interval intersections.
This can be done in a several ways, one is to convert starts and ends, sort them, then do a line sweep with counter.
Another way is to search end index of n + 2 * k, we can do this with a binary search.
Approach
- we also can do a bucket sort for a line sweep, but careful with a zero point
Complexity
-
Time complexity: \(O(nlog(n))\) or O(n)
-
Space complexity: \(O(n)\) or O(1)
Code
fun maximumBeauty(nums: IntArray, k: Int): Int {
val se = mutableListOf<Pair<Int, Int>>()
for (n in nums) { se += (n + k) to 1; se += (n - k) to -1 }
se.sortWith(compareBy({ it.first }, { it.second }))
var cnt = 0
return se.maxOf { cnt -= it.second; cnt }
}
pub fn maximum_beauty(mut nums: Vec<i32>, k: i32) -> i32 {
nums.sort_unstable();
(0..nums.len()).map(|i| {
let (mut lo, mut hi) = (i + 1, nums.len() - 1);
while lo <= hi {
let m = (lo + hi) / 2;
if nums[m] > nums[i] + k + k
{ hi = m - 1 } else { lo = m + 1 }
}; lo - i
}).max().unwrap() as i32
}
int maximumBeauty(vector<int>& nums, int k) {
int d[300002] { 0 }; int res = 1;
for (int n: nums) ++d[n-k+100000], --d[n+k+100001];
for (int i = 0, c = 0; i < 300002; ++i)
res = max(res, c += d[i]);
return res;
}