Merge remote-tracking branch 'origin/main'

Author: BGMer7

src/com/gatsby/_208ImplementTrie.java

@@ -0,0 +1,55 @@
+package com.gatsby;
+
+/**
+ * @author -- gatsby
+ * @date -- 2022/7/12
+ * @description --
+ */
+
+
+public class _208ImplementTrie {
+    class TrieNode {
+        boolean isEnd = false;
+        // 直接创建一个26字母的数组，这样已经可以考虑到所有的下一位字母的情况
+        TrieNode[] children = new TrieNode[26];
+    }
+
+    private TrieNode root;
+
+    public _208ImplementTrie() {
+        root = new TrieNode();
+    }
+
+    public void insert(String word) {
+        TrieNode p = root;
+        for (int i = 0; i < word.length(); ++i) {
+            int letter = word.charAt(i) - 'a';
+            if (p.children[letter] == null) {
+                p.children[letter] = new TrieNode();
+            }
+            p = p.children[letter];
+        }
+        // 此时在最后一个字母，将isEnd置为true
+        p.isEnd = true;
+    }
+
+    public boolean search(String word) {
+        TrieNode p = root;
+        for (int i = 0; i < word.length(); ++i) {
+            int letter = word.charAt(i) - 'a';
+            if (p.children[letter] == null) return false;
+            else p = p.children[letter];
+        }
+        return p.isEnd;
+    }
+
+    public boolean startsWith(String prefix) {
+        TrieNode p = root;
+        for (int i = 0; i < prefix.length(); ++i) {
+            int letter = prefix.charAt(i) - 'a';
+            if (p.children[letter] == null) return false;
+            else p = p.children[letter];
+        }
+        return true;
+    }
+}

src/com/gatsby/_908SmallestRangeI.java

@@ -0,0 +1,20 @@
+package com.gatsby;
+
+/**
+ * @author -- gatsby
+ * @date -- 2022/4/30
+ * @description -- leetcode 908 最小差值
+ */
+
+
+public class _908SmallestRangeI {
+    public int smallestRangeI(int[] nums, int k) {
+        int max = Integer.MIN_VALUE;
+        int min = Integer.MAX_VALUE;
+        for (int num : nums) {
+            if (num > max) max = num;
+            if (num < min) min = num;
+        }
+        return max - min > 2 * k ? max - min - 2 * k : 0;
+    }
+}

src/com/gatsby/offerII/_4OnlyOnce.java

@@ -0,0 +1,40 @@
+package com.gatsby.offerII;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * @author -- gatsby
+ * @date -- 2022/7/13
+ * @description -- 剑指 Offer II 004. 只出现一次的数字
+ */
+
+
+public class _4OnlyOnce {
+    public int singleNumber(int[] nums) {
+        Map<Integer, Integer> count = new HashMap<>();
+        for (int num : nums) {
+            count.put(num, count.getOrDefault(num, 0) + 1);
+        }
+
+        for (int num : count.keySet()) {
+            if (count.get(num) == 1) return num;
+        }
+
+        return -1;
+    }
+
+    public int single(int start, int[] nums) {
+        return nums[start] ^ nums[start + 1] ^ nums[start + 2];
+    }
+
+    public int singleNumberSort(int[] nums) {
+        Arrays.sort(nums);
+
+        for (int i = 0; i + 3 < nums.length; i += 3) {
+            if (nums[i] != nums[i+2]) return single(i, nums);
+        }
+        return -1;
+    }
+}