JunyiCode
4/5/2020 - 2:02 AM

## 169. Majority Element

Divide and Conquer && vote

``````class Solution {
public int majorityElement(int[] nums) {
int count = 0;
int candidate = 0;

for(int num : nums) {
if(count == 0) {
candidate = num;
}

if(candidate == num) {
count++;
} else {
count--;
}
}

return candidate;
}
}``````
``````class Solution {
private int countInRange(int[] nums, int num, int lo, int hi) {
int count = 0;
for (int i = lo; i <= hi; i++) {
if (nums[i] == num) {
count++;
}
}
return count;
}

private int majorityElementRec(int[] nums, int lo, int hi) {
// base case; the only element in an array of size 1 is the majority
// element.
if (lo == hi) {
return nums[lo];
}

// recurse on left and right halves of this slice.
int mid = (hi-lo)/2 + lo;
int left = majorityElementRec(nums, lo, mid);
int right = majorityElementRec(nums, mid+1, hi);

// if the two halves agree on the majority element, return it.
if (left == right) {
return left;
}

// otherwise, count each element and return the "winner".
int leftCount = countInRange(nums, left, lo, hi);
int rightCount = countInRange(nums, right, lo, hi);

return leftCount > rightCount ? left : right;
}

public int majorityElement(int[] nums) {
return majorityElementRec(nums, 0, nums.length-1);
}
}``````
``````class Solution {
public int majorityElement(int[] nums) {
Arrays.sort(nums);
return nums[nums.length/2];
}
}``````
``````class Solution {
public int majorityElement(int[] nums) {
int majorityCount = nums.length/2;

for (int num : nums) {
int count = 0;
for (int elem : nums) {
if (elem == num) {
count += 1;
}
}

if (count > majorityCount) {
return num;
}

}

return -1;
}
}``````
``````/*
hashMap.put(num, hashMap.getOrDefault(num,0)+1);
*/

class Solution {
private Map<Integer, Integer> countNums(int[] nums) {
Map<Integer, Integer> counts = new HashMap<Integer, Integer>();
for (int num : nums) {
if (!counts.containsKey(num)) {
counts.put(num, 1);
}
else {
counts.put(num, counts.get(num)+1);
}
}
return counts;
}

public int majorityElement(int[] nums) {
Map<Integer, Integer> counts = countNums(nums);

Map.Entry<Integer, Integer> majorityEntry = null;
for (Map.Entry<Integer, Integer> entry : counts.entrySet()) {
if (majorityEntry == null || entry.getValue() > majorityEntry.getValue()) {
majorityEntry = entry;
}
}

return majorityEntry.getKey();
}
}``````