剑指OfferII 004. 只出现一次的数字

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;
+    }
+}