An array A consisting of N integers is given. The dominator of array A is the value that occurs in more than half of the elements of A.
For example, consider array A such that
A[0] = 3 A[1] = 4 A[2] = 3 A[3] = 2 A[4] = 3 A[5] = -1 A[6] = 3 A[7] = 3The dominator of A is 3 because it occurs in 5 out of 8 elements of A (namely in those with indices 0, 2, 4, 6 and 7) and 5 is more than a half of 8.
Write a function
class Solution { public int solution(int[] A); }
that, given an array A consisting of N integers, returns index of any element of array A in which the dominator of A occurs. The function should return −1 if array A does not have a dominator.
For example, given array A such that
A[0] = 3 A[1] = 4 A[2] = 3 A[3] = 2 A[4] = 3 A[5] = -1 A[6] = 3 A[7] = 3the function may return 0, 2, 4, 6 or 7, as explained above.
Write an efficient algorithm for the following assumptions:
- N is an integer within the range [0..100,000];
- each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A) {
HashMap<Integer, Integer> hashMap = new HashMap<>();
int dominator = 0;
int count = 0;
for (int i : A) {
if (hashMap.containsKey(i)) {
int tmpCount = hashMap.get(i);
tmpCount++;
hashMap.put(i, tmpCount);
if (tmpCount > count) {
count = tmpCount;
dominator = i;
}
} else hashMap.put(i, 1);
}
if (A.length == 1) return 0;
if (count < (A.length/2)) return -1;
for (int i=0; i<A.length; i++) {
if (A[i] == dominator) return i;
}
return -1;
}
}
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A) {
HashMap<Integer, Integer> hashMap = new HashMap<>();
int dominator = 0;
int count = 0;
for (int i : A) {
if (hashMap.containsKey(i)) {
int tmpCount = hashMap.get(i);
tmpCount++;
hashMap.put(i, tmpCount);
if (tmpCount > count) {
count = tmpCount;
dominator = i;
}
} else hashMap.put(i, 1);
}
if (A.length == 1) return 0;
if (count < (A.length/2)) return -1;
for (int i=0; i<A.length; i++) {
if (A[i] == dominator) return i;
}
return -1;
}
}
// you can also use imports, for example:
import java.util.*;
// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");
class Solution {
public int solution(int[] A) {
HashMap<Integer, Integer> hashMap = new HashMap<>();
int dominator = 0;
int count = 0;
for (int i : A) {
if (hashMap.containsKey(i)) {
int tmpCount = hashMap.get(i);
tmpCount++;
hashMap.put(i, tmpCount);
if (tmpCount > count) {
count = tmpCount;
dominator = i;
}
} else hashMap.put(i, 1);
}
if (A.length == 1) return 0;
if (count < (A.length/2)) return -1;
for (int i=0; i<A.length; i++) {
if (A[i] == dominator) return i;
}
return -1;
}
}
The following issues have been detected: wrong answers.
For example, for the input [2, 1, 1, 3] the solution returned a wrong answer (got 1, but element is not a dominator, value 1 has only 2 occurences (n=4)).
half elements the same, and half + 1 elements the same
got 10, but element is not a dominator, value 2 has only 10 occurences (n=20)
array with exactly N/2 values 1, N even + [0,0,1,1,1]
got 1, but element is not a dominator, value 1 has only 2 occurences (n=4)
array with exactly floor(N/2) values 1, N odd + [0,0,1,1,1]
got 1, but element is not a dominator, value 1 has only 2 occurences (n=5)