algorithm001 · GeekUniversity · May 13, 2019 · May 12, 2019
diff --git a/Week_04/id_88/Leetcode_169_088.cpp b/Week_04/id_88/Leetcode_169_088.cpp
@@ -0,0 +1,64 @@
+//对nums进行排序，排序后的中位数就是答案
+//使用了归并排序算法
+
+class Solution {
+public:
+	int majorityElement(vector<int>& nums) {
+		mergeSort(nums, 0, nums.size() - 1);
+		return nums[nums.size() / 2];
+	}
+
+private:
+	void mergeSort(vector<int>& nums, int start, int end) {
+		if (start >= end) return;
+
+		int middle = (end + start) / 2;
+
+		mergeSort(nums, start, middle);
+		mergeSort(nums, middle+1, end);
+		merge(nums, start, middle, end);
+
+	}
+
+	void merge(vector<int>& nums, int start, int middle, int end) {
+		vector<int> temp;
+		int p = start, q = middle + 1;
+
+		while (p <= middle && q <= end) {
+	        if (nums[p] <= nums[q])
+			{
+				temp.push_back(nums[p]);
+				p++;
+			}
+			else {
+				temp.push_back(nums[q]);
+				q++;
+			}
+		}
+
+		if (p > middle)
+		{
+			while (q <= end)
+			{
+				temp.push_back(nums[q]);
+				q++;
+			}
+		}
+
+		if (q > end)
+		{
+			while (p <= middle)
+			{
+				temp.push_back(nums[p]);
+				p++;
+			}
+		}
+
+		for (int each : temp)
+		{
+			nums[start] = each;
+			start++;
+		}
+
+	}
+};
diff --git a/Week_04/id_88/Leetcode_720_088.cpp b/Week_04/id_88/Leetcode_720_088.cpp
@@ -0,0 +1,78 @@
+class TrieNode {
+public:
+	bool isWord;
+	TrieNode* children[26];
+	TrieNode():isWord(false) {
+		for (int i = 0; i < 26; i++)
+		{
+			children[i] = NULL;
+		}
+	}
+
+	~TrieNode() {
+		for (int i = 0; i < 26; i++)
+		{
+			if (children[i] != NULL) delete children[i];
+		}
+	}
+};
+
+class Solution {
+public:
+	string longestWord(vector<string>& words) {
+
+		if (words.size() == 0) return "";
+
+        //构建Trie树
+		for (int i = 0; i < words.size(); i++)
+		{
+			addWord(words[i]);
+		}
+
+		string ret = "";
+		result = "";
+
+        //使用Trie树深度优先遍历查找出最长的单词
+		findLongestWord(root, ret);
+
+		return result;
+	}
+
+	void addWord(string& word)
+	{
+		if (root == NULL) root = new TrieNode();
+        TrieNode* ptr = root;
+
+		for (char ch : word)
+		{
+			if(ptr->children[ch - 'a'] == NULL) ptr->children[ch - 'a'] = new TrieNode();
+
+			ptr = ptr->children[ch - 'a'];
+
+		}
+
+		ptr->isWord = true;
+	}
+
+	void findLongestWord(TrieNode* root, string str) {
+		if (root != NULL)
+		{
+			for (int i = 0; i < 26; i++)
+			{
+				if (root->children[i] != NULL && root->children[i]->isWord == true)
+				{
+					string newStr = str + (char)('a' + i);
+					if (newStr.size() > result.size()) {
+						result = newStr;
+					}
+					findLongestWord(root->children[i], newStr);
+				}
+			}
+		}
+	}
+
+private:
+	TrieNode * root;
+	string result;
+	int longestLength;
+};