Tasks
4. MinAbsSumOfTwo in codility (Lesson 15)
: Find the minimal absolute value of a sum of two elements.
My first answer
- It occurred timeout error…
- Time complexity: O(N * N) (No~~~~~😫)
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import java.lang.Math;
class Solution {
// (P, Q) -> |A[P] + A[Q]|, 0 ≤ P ≤ Q < N
// 1. set a -> for
// 2. set b -> for ** I wondered multiple for loop is okay for time complexity?
// 3. get a + b and make it to the absolute value
// 4. compare the previous value -> if the current is smaller, save to variable
// 5. return the last value
private int min = 0;
public int solution(int[] A) {
min = Math.abs(A[0] + A[0]);
for (int a : A) {
for (int b : A) {
if (min > Math.abs(a + b)) min = Math.abs(a + b);
}
}
return min;
}
}
Final answer
⭐️ The point
- Don’t use only for loop -> I thought two for loop is okay lol -> Let’s avoid two for loop, too!!
- Don’t forget this problem is related with caterpillar method algorithm
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import java.util.Arrays;
import java.lang.Math;
class Solution {
public int solution(int[] A) {
int min = Integer.MAX_VALUE;
int p = 0;
int q = A.length - 1;
Arrays.sort(A);
while (p <= q) { // the other way of for loop
int current = A[p] + A[q];
min = Math.min(min, Math.abs(current));
// caterpillar method
if (current < 0) p++; // -
else q--; // +
}
return min;
}
}
Question
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Let A be a non-empty array consisting of N integers.
The abs sum of two for a pair of indices (P, Q) is the absolute value |A[P] + A[Q]|, for 0 ≤ P ≤ Q < N.
For example, the following array A:
A[0] = 1
A[1] = 4
A[2] = -3
has pairs of indices (0, 0), (0, 1), (0, 2), (1, 1), (1, 2), (2, 2).
The abs sum of two for the pair (0, 0) is A[0] + A[0] = |1 + 1| = 2.
The abs sum of two for the pair (0, 1) is A[0] + A[1] = |1 + 4| = 5.
The abs sum of two for the pair (0, 2) is A[0] + A[2] = |1 + (−3)| = 2.
The abs sum of two for the pair (1, 1) is A[1] + A[1] = |4 + 4| = 8.
The abs sum of two for the pair (1, 2) is A[1] + A[2] = |4 + (−3)| = 1.
The abs sum of two for the pair (2, 2) is A[2] + A[2] = |(−3) + (−3)| = 6.
the function should return 1, as explained above.
Write an efficient algorithm for the following assumptions:
- N is an integer within the range [1..100,000];
- each element of array A is an integer within the range [−1,000,000,000..1,000,000,000].
New words
- indices : multiple indexes
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