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package leetcode.easy;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import utils.NthElement;
public class P_169 {
// HashMap -> O(n) time O(n) space
public int majorityElement1(int[] nums) {
final Map<Integer, Integer> count = new HashMap<>();
for (int num : nums) {
count.merge(num, 1, Integer::sum);
if (count.get(num) > nums.length / 2) {
return num;
}
}
return -1;
}
// Randomization -> O(n) time O(1) space
public int majorityElement2(int[] nums) {
final Random r = new Random();
while (true) {
final int idx = r.nextInt(nums.length);
final int majority = nums[idx];
int count = 0;
for (int num : nums) {
if (num == majority && ++count > nums.length / 2) {
return num;
}
}
}
}
// Bit Vote -> O(32*n) time O(1) space
public int majorityElement3(int[] nums) {
int res = 0;
for (int i = 0; i < Integer.SIZE; i++) {
int count = 0;
for (int num : nums) {
final int mask = 1 << i;
if ((num & mask) != 0) {
count++;
}
if (count > nums.length / 2) {
res |= mask;
}
}
}
return res;
}
// Boyer-Moore vote -> O(n) time O(1) space
public int majorityElement4(int[] nums) {
int counter = 0, majority = 0;
for (int num : nums) {
if (counter == 0) {
majority = num;
counter = 1;
} else if (majority == num) {
counter++;
} else {
counter--;
}
}
return majority;
}
// Sort -> O(n log n) time O(1) space
public int majorityElement5(int[] nums) {
Arrays.sort(nums);
return nums[nums.length / 2];
}
// Partial Sort -> O(n) average // O(n^2) worst time O(1) space
public int majorityElement6(int[] nums) {
return NthElement.findKthLargest(nums, nums.length / 2 + 1);
}
// Divide and Conquer -> O(n log n) time O(log n) space (call stack)
public int majorityElement7(int[] nums) {
return majorityElement(nums, 0, nums.length - 1);
}
private static int majorityElement(int[] nums, int left, int right) {
if (left == right) {
return nums[left];
}
final int mid = left + right >>> 1;
final int ml = majorityElement(nums, left, mid);
final int mr = majorityElement(nums, mid + 1, right);
if (ml == mr) {
return ml;
}
int c1 = 0, c2 = 0;
for (int i = left; i <= right; i++) {
if (nums[i] == ml) {
c1++;
}
if (nums[i] == mr) {
c2++;
}
}
return c1 > c2 ? ml : mr;
}
}