algo for week24

README.md

@@ -18,6 +18,7 @@ Algorithm、Review、Tip、Share
 |98|[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)|[Java](./week20/algo/lc98/Solution.java)|Medium|
 |182|[Duplicate Emails](https://leetcode.com/problems/duplicate-emails/)|[SQL](./week01/algo/lc182/leetcode182.sql)|Easy|
 |101|[Symmetric Tree](https://leetcode.com/problems/symmetric-tree/)|[Java](./week12/algo/lc101/Solution.java)|Easy|
+|169|[Majority Element](https://leetcode.com/problems/majority-element/)|[Java](./week24/algo/lc169/Solution.java)|Easy|
 |226|[Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/)|[Java](./week10/algo/lc226/Solution.java)|Easy|
 |227|[Basic Calculator II](https://leetcode.com/problems/basic-calculator-ii/)|[Java](./week08/algo/lc227/Calculator.java)|Medium|
 |232|[Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks/)|[Java](./week09/algo/lc232/MyQueue.java)|Easy|

week24/algo/lc169/Solution.java

@@ -0,0 +1,55 @@
+package com.milley.majorityelement;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class Solution {
+    public int majorityElement(int[] nums) {
+        Map<Integer, Integer> majorityMap = new HashMap<>(nums.length);
+        for (int num : nums) {
+            Integer val = majorityMap.get(num);
+            majorityMap.put(num, val == null ? 1 : val.intValue() + 1);
+        }
+
+        for (Map.Entry<Integer, Integer> entry : majorityMap.entrySet()) {
+            if (entry.getValue() > nums.length / 2) {
+                return entry.getKey();
+            }
+        }
+        return 0;
+    }
+
+    public int majorityElementBySort(int[] nums) {
+        Arrays.sort(nums);
+        int eqLen = 0;
+        for (int i = 0; i < nums.length - 1; i++) {
+            if (nums[i] == nums[i + 1]) {
+                eqLen++;
+            } else {
+                if (eqLen > nums.length / 2 - 1) {
+                    return nums[i];
+                } else {
+                    eqLen = 0;
+                }
+            }
+        }
+        return nums[eqLen];
+    }
+
+    public int majorityElementByMagic(int[] nums) {
+        Arrays.sort(nums);
+        return nums[nums.length / 2];
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println(solution.majorityElement(new int[]{3, 2, 3}));
+        System.out.println(solution.majorityElement(new int[]{2, 2, 1, 1, 1, 2, 2}));
+        System.out.println(solution.majorityElementBySort(new int[]{3, 2, 3}));
+        System.out.println(solution.majorityElementBySort(new int[]{-1, 1, 1, 1, 2, 1}));
+        System.out.println(solution.majorityElementByMagic(new int[]{3, 2, 3}));
+        System.out.println(solution.majorityElementByMagic(new int[]{-1, 1, 1, 1, 2, 1}));
+    }
+}