From 34e7e015c77c06d1c34dca67f7a23899299cd101 Mon Sep 17 00:00:00 2001
From: zeekling <lingzhaohui@zeekling.cn>
Date: Sun, 29 Nov 2020 16:24:03 +0800
Subject: [PATCH] =?UTF-8?q?=E5=8F=AA=E5=87=BA=E7=8E=B0=E4=B8=80=E6=AC=A1?=
 =?UTF-8?q?=E7=9A=84=E6=95=B0=E5=AD=97?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../java/com/leetcode/array/SingleNumber.java | 53 +++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 src/main/java/com/leetcode/array/SingleNumber.java

diff --git a/src/main/java/com/leetcode/array/SingleNumber.java b/src/main/java/com/leetcode/array/SingleNumber.java
new file mode 100644
index 0000000..80fe2b7
--- /dev/null
+++ b/src/main/java/com/leetcode/array/SingleNumber.java
@@ -0,0 +1,53 @@
+package com.leetcode.array;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * 只出现一次的数字
+给定一个非空整数数组，除了某个元素只出现一次以外，其余每个元素均出现两次。找出那个只出现了一次的元素。
+
+说明：
+
+你的算法应该具有线性时间复杂度。 你可以不使用额外空间来实现吗？
+
+示例 1:
+
+输入: [2,2,1]
+输出: 1
+示例 2:
+
+输入: [4,1,2,1,2]
+输出: 4
+
+作者：力扣 (LeetCode)
+链接：https://leetcode-cn.com/leetbook/read/top-interview-questions/xm0u83/
+来源：力扣（LeetCode）
+著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。
+ */
+public class SingleNumber {
+    
+
+    public int singleNumber(int[] nums) {
+        Map<Integer, Integer> map = new HashMap<>();
+
+        for (int i = 0; i < nums.length; i++) {
+            Integer counter = map.getOrDefault(nums[i], 0);
+            counter ++;
+            map.put(nums[i], counter);
+        }
+        for (Map.Entry<Integer, Integer> entry: map.entrySet()) {
+            if (entry.getValue() == 1) {
+                return entry.getKey();
+            }
+        }
+        return 0;
+    }
+
+    public static void main(String[] args) {
+        SingleNumber singleNumber = new SingleNumber();
+        int[] nums = {2,2,1};
+        int res = singleNumber.singleNumber(nums);
+        System.out.println(res);
+    }
+}
-- 
2.45.2