LeetCode - Majority Element II
Problem description
Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times.
Note: The algorithm should run in linear time and in O(1) space.
Example 1:
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Input: [3,2,3]
Output: [3]
Example 2:
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Input: [1,1,1,3,3,2,2,2]
Output: [1,2]
Analysis
Basically, it’s another type of Boyer-Moore Majority Vote algorithm.
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class Solution {
public List<Integer> majorityElement(int[] nums) {
if (nums == null || nums.length == 0)
return new ArrayList<Integer>();
List<Integer> result = new ArrayList<Integer>();
int number1 = nums[0], number2 = nums[0], count1 = 0, count2 = 0, len = nums.length;
for (int i = 0; i < len; i++) {
if (nums[i] == number1)
count1++;
else if (nums[i] == number2)
count2++;
else if (count1 == 0) {
number1 = nums[i];
count1 = 1;
} else if (count2 == 0) {
number2 = nums[i];
count2 = 1;
} else {
count1--;
count2--;
}
}
count1 = 0;
count2 = 0;
for (int i = 0; i < len; i++) {
if (nums[i] == number1)
count1++;
else if (nums[i] == number2)
count2++;
}
if (count1 > len / 3)
result.add(number1);
if (count2 > len / 3)
result.add(number2);
return result;
}
}