Tasks Details
easy
1.
EquiLeader
Find the index S such that the leaders of the sequences A[0], A[1], ..., A[S] and A[S + 1], A[S + 2], ..., A[N - 1] are the same.
Task Score
100%
Correctness
100%
Performance
100%
A non-empty array A consisting of N integers is given.
The leader of this array is the value that occurs in more than half of the elements of A.
An equi leader is an index S such that 0 ≤ S < N − 1 and two sequences A[0], A[1], ..., A[S] and A[S + 1], A[S + 2], ..., A[N − 1] have leaders of the same value.
For example, given array A such that:
A[0] = 4 A[1] = 3 A[2] = 4 A[3] = 4 A[4] = 4 A[5] = 2we can find two equi leaders:
- 0, because sequences: (4) and (3, 4, 4, 4, 2) have the same leader, whose value is 4.
- 2, because sequences: (4, 3, 4) and (4, 4, 2) have the same leader, whose value is 4.
The goal is to count the number of equi leaders.
Write a function:
class Solution { public int solution(int[] A); }
that, given a non-empty array A consisting of N integers, returns the number of equi leaders.
For example, given:
A[0] = 4 A[1] = 3 A[2] = 4 A[3] = 4 A[4] = 4 A[5] = 2the function should return 2, 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].
Copyright 2009–2025 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used Java 21
Time spent on task 89 minutes
Notes
not defined yet
Code: 13:29:24 UTC,
java,
autosave
Code: 13:29:28 UTC,
java,
verify,
result: Passed
import java.util.*;
class Solution {
public int solution(int[] A) {
Map<Integer, Integer> firstCountMap = new HashMap<>();
Map<Integer, Integer> secondCountMap = new HashMap<>();
int firstLeader = A[0];
int secondLeader = A[0];
int count = 0;
for (int a : A) {
secondCountMap.put(a, secondCountMap.getOrDefault(a, 0) + 1);
if (secondCountMap.get(secondLeader) < secondCountMap.get(a)) {
secondLeader = a;
}
}
if (secondCountMap.get(secondLeader) <= A.length / 2) {
return count;
}
for (int i=0; i<A.length-1; i++) {
firstCountMap.put(A[i], firstCountMap.getOrDefault(A[i], 0) + 1);
secondCountMap.put(A[i], secondCountMap.get(A[i]) - 1);
if (firstCountMap.get(firstLeader) < firstCountMap.get(A[i])) {
firstLeader = A[i];
}
if (secondCountMap.get(secondLeader) < secondCountMap.get(A[i])) {
secondLeader = A[i];
}
if (firstCountMap.get(firstLeader) > (i + 1) / 2.0 && secondCountMap.get(secondLeader) > (A.length - i - 1) / 2.0 && firstLeader == secondLeader) {
count++;
}
}
return count;
}
}
Analysis
Code: 13:49:00 UTC,
java,
verify,
result: Passed
import java.util.*;
class Solution {
public int solution(int[] A) {
Map<Integer, Integer> firstCountMap = new HashMap<>();
Map<Integer, Integer> secondCountMap = new HashMap<>();
int firstLeader = A[0];
int secondLeader = A[0];
int count = 0;
for (int a : A) {
secondCountMap.put(a, secondCountMap.getOrDefault(a, 0) + 1);
if (secondCountMap.get(secondLeader) < secondCountMap.get(a)) {
secondLeader = a;
}
}
if (secondCountMap.get(secondLeader) <= A.length / 2) {
return count;
}
for (int i=0; i<A.length-1; i++) {
firstCountMap.put(A[i], firstCountMap.getOrDefault(A[i], 0) + 1);
secondCountMap.put(A[i], secondCountMap.get(A[i]) - 1);
if (firstCountMap.get(firstLeader) < firstCountMap.get(A[i])) {
firstLeader = A[i];
}
if (secondCountMap.get(secondLeader) < secondCountMap.get(A[i])) {
secondLeader = A[i];
}
if (firstCountMap.get(firstLeader) > (i + 1) / 2.0 && secondCountMap.get(secondLeader) > (A.length - i - 1) / 2.0 && firstLeader == secondLeader) {
count++;
}
}
return count;
}
}
Analysis
Code: 14:14:07 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
Map<Integer, Integer> firstCountMap = new HashMap<>();
Map<Integer, Integer> secondCountMap = new HashMap<>();
int firstLeader = A[0];
int secondLeader = A[0];
int count = 0;
for (int a : A) {
secondCountMap.put(a, secondCountMap.getOrDefault(a, 0) + 1);
if (secondCountMap.get(secondLeader) < secondCountMap.get(a)) {
secondLeader = a;
}
}
if (secondCountMap.get(secondLeader) <= A.length / 2) {
return count;
}
for (int i=0; i<A.length-1; i++) {
firstCountMap.put(A[i], firstCountMap.getOrDefault(A[i], 0) + 1);
secondCountMap.put(A[i], secondCountMap.get(A[i]) - 1);
if (firstCountMap.get(firstLeader) < firstCountMap.get(A[i])) {
firstLeader = A[i];
}
if (secondCountMap.get(secondLeader) < secondCountMap.get(A[i])) {
secondLeader = A[i];
}
if (firstCountMap.get(firstLeader) > (i + 1) / 2.0 && secondCountMap.get(secondLeader) > (A.length - i - 1) / 2.0 && firstLeader == secondLeader) {
count++;
}
}
return count;
}
}
Code: 14:26:54 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
Map<Integer, Integer> firstCountMap = new HashMap<>();
Map<Integer, Integer> secondCountMap = new HashMap<>();
int firstLeader = A[0];
int secondLeader = A[0];
int count = 0;
for (int a : A) {
secondCountMap.put(a, secondCountMap.getOrDefault(a, 0) + 1);
if (secondCountMap.get(secondLeader) < secondCountMap.get(a)) {
secondLeader = a;
}
}
if (secondCountMap.get(secondLeader) <= A.length / 2) {
return count;
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:28:41 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
Map<Integer, Integer> firstCountMap = new HashMap<>();
Map<Integer, Integer> secondCountMap = new HashMap<>();
int firstLeader = A[0];
int secondLeader = A[0];
int count = 0;
for (int a : A) {
}
if (secondCountMap.get(secondLeader) <= A.length / 2) {
return count;
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:28:51 UTC,
java,
autosave
Code: 14:48:56 UTC,
java,
autosave
Code: 14:49:11 UTC,
java,
autosave
Code: 14:49:41 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} el
}
if (secondCountMap.get(secondLeader) <= A.length / 2) {
return count;
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:50:01 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
if (secondCountMap.get(secondLeader) <= A.length / 2) {
return count;
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:50:22 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
if (secondCountMap.get(secondLeader) <= A.length / 2) {
return count;
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:51:39 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
i
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:51:49 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
if (size > 0) {
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:52:19 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size > 0) {
if
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:52:33 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size > 0) {
for (int a : A) {
if ()
leaderCount++;
}
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:52:44 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size > 0) {
for (int a : A) {
if (value == a)
leaderCount++;
}
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:53:15 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a)
leaderCount++;
}
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:53:26 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value =
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:53:40 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:54:11 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
for (int a ) {
}
for (int i=0; i<A.length-1; i++) {
}
return count;
}
}
Code: 14:54:29 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
for (int a : A) {
if () {
}
}
return count;
}
}
Code: 14:54:39 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
for (int a : A) {
if (a == )
if () {
}
}
return count;
}
}
Code: 14:54:58 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
for (int a : A) {
if (a == )
if () {
}
}
return count;
}
}
Code: 14:55:10 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
for (int a : A) {
if (value == a) {
}
if () {
}
}
return count;
}
}
Code: 14:55:38 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int a : A) {
if (value == a) {
firstLeaderCount++;
}
if (leaderCount - ) {
count++;
}
}
return count;
}
}
Code: 14:55:49 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int a : A) {
if (value == a) {
firstLeaderCount++;
}
if (leaderCount) {
count++;
}
}
return count;
}
}
Code: 14:56:04 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int a : A) {
if (value == a) {
firstLeaderCount++;
}
if (firstLeaderCount > ) {
count++;
}
}
return count;
}
}
Code: 14:56:35 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int i=0; i<A.length; i++) {
if (value == a) {
firstLeaderCount++;
}
if (firstLeaderCount > (i + 1) / 2.0 ) {
count++;
}
}
return count;
}
}
Code: 14:57:06 UTC,
java,
autosave
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int i=0; i<A.length; i++) {
if (value == a) {
firstLeaderCount++;
}
if (firstLeaderCount > (i + 1) / 2.0 && leaderCount - firstLeaderCount > A.length - i - 1 / 2.0 ) {
count++;
}
}
return count;
}
}
Code: 14:57:12 UTC,
java,
verify,
result: Failed
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int i=0; i<A.length; i++) {
if (value == a) {
firstLeaderCount++;
}
if (firstLeaderCount > (i + 1) / 2.0 && leaderCount - firstLeaderCount > (A.length - i - 1) / 2.0 ) {
count++;
}
}
return count;
}
}
Analysis
Compile error
Solution.java:32: error: cannot find symbol if (value == a) { ^ symbol: variable a location: class Solution 1 error
Code: 14:57:20 UTC,
java,
verify,
result: Passed
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int i=0; i<A.length; i++) {
if (value == A[i]) {
firstLeaderCount++;
}
if (firstLeaderCount > (i + 1) / 2.0 && leaderCount - firstLeaderCount > (A.length - i - 1) / 2.0) {
count++;
}
}
return count;
}
}
Analysis
Code: 14:57:28 UTC,
java,
verify,
result: Passed
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int i=0; i<A.length; i++) {
if (value == A[i]) {
firstLeaderCount++;
}
if (firstLeaderCount > (i + 1) / 2.0 && leaderCount - firstLeaderCount > (A.length - i - 1) / 2.0) {
count++;
}
}
return count;
}
}
Analysis
Code: 14:57:33 UTC,
java,
final,
score: 
100
import java.util.*;
class Solution {
public int solution(int[] A) {
int count = 0;
int size = 0;
int value = 0;
for (int a : A) {
if (size == 0) {
value = a;
size++;
} else if (value == a) {
size++;
} else {
size--;
}
}
int leaderCount = 0;
if (size == 0) {
return 0;
} else {
for (int a : A) {
if (value == a) {
leaderCount++;
}
}
}
int firstLeaderCount = 0;
for (int i=0; i<A.length; i++) {
if (value == A[i]) {
firstLeaderCount++;
}
if (firstLeaderCount > (i + 1) / 2.0 && leaderCount - firstLeaderCount > (A.length - i - 1) / 2.0) {
count++;
}
}
return count;
}
}
Analysis summary
The solution obtained perfect score.
Analysis
Detected time complexity:
O(N)
expand all
Correctness tests
1.
0.004 s
OK
2.
0.004 s
OK
3.
0.004 s
OK
1.
0.004 s
OK
2.
0.004 s
OK
3.
0.004 s
OK
1.
0.004 s
OK
2.
0.004 s
OK
1.
0.004 s
OK
1.
0.008 s
OK