[Link] https://app.codility.com/programmers/trainings/4/array_inversion_count/
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import java.util.*;
class Solution {
public int solution(int[] A) {
ArrayList<Integer> list = new ArrayList<>();
int cnt = 0;
list.add(A[0]);
for(int i = 1; i < A.length; i++) {
int insertIdx = findIdx(list, A[i]);
if(insertIdx == list.size()) list.add(A[i]);
else list.add(insertIdx, A[i]);
cnt += insertIdx;
}
return cnt;
}
public int findIdx(ArrayList<Integer> list, int val) {
int l = 0, r = list.size() - 1, mid;
while(l <= r) {
mid = (l + r) / 2;
if(list.get(mid) > val) l = mid + 1;
else if(list.get(mid) == val) return mid;
else r = mid - 1;
}
return l;
}
}