Merge pull request #243 from AAluoxiang/master

第四周作业#1

Author: GeekUniversity

Week_04/id_1/LeetCode_169_1.java

@@ -0,0 +1,32 @@
+package week01;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Auth:luoxiang
+ * Time:2019/6/30 5:31 PM
+ * Desc:    求众数
+ */
+public class LeetCode_169_1 {
+
+    public static void main(String[] args) {
+        System.out.println(new LeetCode_169_1().majorityElement(new int[]{3,2,3}));
+        System.out.println(new LeetCode_169_1().majorityElement(new int[]{2,2,1,1,1,2,2}));
+    }
+
+    public int majorityElement(int[] nums) {
+        if (nums == null || nums.length == 0) return 0;
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int num : nums) {
+            int temp = map.getOrDefault(num, 0) + 1;
+            if (temp <= (nums.length / 2)) {
+                map.put(num, map.getOrDefault(num, 0) + 1);
+            } else {
+                return num;
+            }
+
+        }
+        throw new IllegalArgumentException("异常");
+    }
+}

Week_04/id_1/LeetCode_198_1.java

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+package week04;
+
+/**
+ * Auth:luoxiang
+ * Time:2019/6/30 5:46 PM
+ * Desc:    DP 打家劫舍
+ */
+public class LeetCode_198_1 {
+    public static void main(String[] args) {
+        System.out.println(new LeetCode_198_1().rob(new int[]{1,2,3,1}));
+        System.out.println(new LeetCode_198_1().rob(new int[]{2,7,9,3,1}));
+    }
+
+    public int rob(int[] nums) {
+        int len = nums.length;
+        if (len == 0 || len == 1) return len == 0 ? 0 : nums[0];
+        int[] dp = new int[len];
+        dp[0]=nums[0];
+        dp[1]=Math.max(nums[0],nums[1]);
+        for(int i=2;i<len;i++){
+            dp[i]=Math.max(dp[i-1],dp[i-2]+nums[i]);
+        }
+        return dp[len-1];
+    }
+}

Week_04/id_1/LeetCode_208_1.java

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+class Trie {
+
+    TrieNode root;
+    class TrieNode{
+        char val;
+        TrieNode [] child=new TrieNode[26];
+        boolean isWord=false;
+        public TrieNode(){}
+        public  TrieNode(char val){
+            TrieNode node = new TrieNode();
+            node.val=val;
+        }
+    }
+
+    /** Initialize your data structure here. */
+    public Trie() {
+        root=new TrieNode();
+    }
+
+    /** Inserts a word into the trie. */
+    public void insert(String word) {
+        TrieNode node = this.root;
+        for (char c : word.toCharArray()) {
+            if(node.child[c-'a']==null){
+                node.child[c-'a']=new TrieNode(c);
+            }
+            node=node.child[c-'a'];
+        }
+        node.isWord=true;
+    }
+
+    /** Returns if the word is in the trie. */
+    public boolean search(String word) {
+        TrieNode node = this.root;
+        for (char c : word.toCharArray()) {
+            if(node.child[c-'a']==null){
+                return false;
+            }
+            node=node.child[c-'a'];
+        }
+        return node.isWord;
+    }
+
+    /** Returns if there is any word in the trie that starts with the given prefix. */
+    public boolean startsWith(String prefix) {
+        TrieNode node = this.root;
+        for (char c : prefix.toCharArray()) {
+            if(node.child[c-'a']==null){
+                return false;
+            }
+            node=node.child[c-'a'];
+
+        }
+        return true;
+    }
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * Trie obj = new Trie();
+ * obj.insert(word);
+ * boolean param_2 = obj.search(word);
+ * boolean param_3 = obj.startsWith(prefix);
+ */

Week_04/id_1/LeetCode_455_1.java

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+package week01;
+
+import java.util.Arrays;
+
+/**
+ * Auth:luoxiang
+ * Time:2019/6/30 5:54 PM
+ * Desc:
+ */
+public class LeetCode_455_1 {
+    public static void main(String[] args) {
+        System.out.println(new LeetCode_455_1().findContentChildren(new int[]{1,2},new int[]{1,2,3}));
+        System.out.println(new LeetCode_455_1().findContentChildren(new int[]{1,2,3},new int[]{1,1}));
+    }
+
+    public int findContentChildren(int[] g, int[] s) {
+        if (g.length == 0 || s.length == 0) return 0;
+        // g 与 s 排序
+        Arrays.sort(g);
+        Arrays.sort(s);
+        int count=0;
+        int gi=0,si=0;
+        while (gi<g.length && si<s.length){
+            if(g[gi]<=s[si]){
+                count++;
+                gi++;si++;
+            }else{
+                si++;
+            }
+        }
+        return count;
+    }
+}

Week_04/id_1/LeetCode_70_1.java

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+package week01;
+
+/**
+ * Auth:luoxiang
+ * Time:2019/6/30 5:17 PM
+ * Desc:    爬楼梯
+ */
+public class LeetCode_70_1 {
+
+    public static void main(String[] args) {
+        System.out.println(new LeetCode_70_1().climbStairs(3));
+    }
+
+    public int climbStairs(int n) {
+        if(n<3) return n;
+        int[] dp = new int[n + 1];
+        dp[1]=1;
+        dp[2]=2;
+        for(int i=3;i<=n;i++){
+            dp[i]=dp[i-1]+dp[i-2];
+        }
+        return dp[n];
+
+    }
+}

Week_04/id_1/LeetCode_720_1.java

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+package week01;
+
+import java.util.Arrays;
+
+public class LeetCode_720_1 {
+    public static void main(String[] args) {
+        System.out.println(new LeetCode_720_1().longestWord(new String[]{"w","wo","wor","worl", "world"}));
+    }
+
+    public String longestWord(String[] words) {
+        if (words == null || words.length == 0) return "";
+        Arrays.sort(words);
+        int len = 0;
+        for (String word : words) {
+            len=Math.max(len,word.length());
+        }
+        for (int i = len; i > 0; i--) {
+            for (int j = 0; j < words.length; j++) {
+                if (words[j].length() == i) {
+                    int temp = i;
+                    for (int k = j - 1; k >= 0; k--) {
+                        if (words[j].substring(0, temp - 1).equals(words[k])) {
+                            temp--;
+                        }
+                    }
+                    if (temp == 1) return words[j];
+                }
+            }
+        }
+        return "";
+    }
+}