diff --git a/.idea/dataSources.xml b/.idea/dataSources.xml
new file mode 100644
index 0000000000000000000000000000000000000000..55fd1b9185aee533d1f896d89006003219c258ee
--- /dev/null
+++ b/.idea/dataSources.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="DataSourceManagerImpl" format="xml" multifile-model="true">
+    <data-source source="LOCAL" name="本地环境" uuid="e90f08b5-9682-409c-b239-62c25d77fd41">
+      <driver-ref>mysql.8</driver-ref>
+      <synchronize>true</synchronize>
+      <jdbc-driver>com.mysql.cj.jdbc.Driver</jdbc-driver>
+      <jdbc-url>jdbc:mysql://localhost:3306/leetcode</jdbc-url>
+      <working-dir>$ProjectFileDir$</working-dir>
+      <driver-properties>
+        <property name="useSSL" value="FALSE" />
+      </driver-properties>
+    </data-source>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/inspectionProfiles/Project_Default.xml b/.idea/inspectionProfiles/Project_Default.xml
index 787303afb4ead6f0babd85ba4953793011502ade..1db5c797a9befceed0716de257e0dad378b893be 100644
--- a/.idea/inspectionProfiles/Project_Default.xml
+++ b/.idea/inspectionProfiles/Project_Default.xml
@@ -2,6 +2,8 @@
   <profile version="1.0">
     <option name="myName" value="Project Default" />
     <inspection_tool class="AlibabaClassMustHaveAuthor" enabled="false" level="MAJOR" enabled_by_default="false" />
+    <inspection_tool class="AlibabaRemoveCommentedCode" enabled="false" level="MAJOR" enabled_by_default="false" />
+    <inspection_tool class="CommentedOutCode" enabled="false" level="WEAK WARNING" enabled_by_default="false" />
     <inspection_tool class="JavaDoc" enabled="true" level="WARNING" enabled_by_default="true">
       <option name="TOP_LEVEL_CLASS_OPTIONS">
         <value>
diff --git a/.idea/runConfigurations.xml b/.idea/runConfigurations.xml
new file mode 100644
index 0000000000000000000000000000000000000000..797acea53eb091cf5b30518802c3073f544adeed
--- /dev/null
+++ b/.idea/runConfigurations.xml
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RunConfigurationProducerService">
+    <option name="ignoredProducers">
+      <set>
+        <option value="com.android.tools.idea.compose.preview.runconfiguration.ComposePreviewRunConfigurationProducer" />
+      </set>
+    </option>
+  </component>
+</project>
\ No newline at end of file
diff --git a/src/main/java/cn/hy/entity/ListNode.java b/src/main/java/cn/hy/entity/ListNode.java
new file mode 100644
index 0000000000000000000000000000000000000000..779d893dae9fd8cfc644fadc6811856ac89c819e
--- /dev/null
+++ b/src/main/java/cn/hy/entity/ListNode.java
@@ -0,0 +1,19 @@
+package cn.hy.entity;
+
+/**
+ * 用于leetcode题库第 2 题的链表实现类
+ */
+public class ListNode {
+    public int val;
+    public ListNode next;
+    public ListNode(){}
+
+    public ListNode(int val) {
+        this.val = val;
+    }
+
+    public ListNode(int val, ListNode next) {
+        this.val = val;
+        this.next = next;
+    }
+}
diff --git a/src/main/java/cn/hy/leetcode/Solution.java b/src/main/java/cn/hy/leetcode/Solution.java
index 53eefa41192ba9a783c6afa0c202aa1a1adacf96..dc5810391356d9387f33197c57afd3f7fe8822b5 100644
--- a/src/main/java/cn/hy/leetcode/Solution.java
+++ b/src/main/java/cn/hy/leetcode/Solution.java
@@ -1,5 +1,6 @@
 package cn.hy.leetcode;
 
+import cn.hy.entity.ListNode;
 import cn.hy.util.StringUtil;
 import lombok.extern.log4j.Log4j2;
 import lombok.extern.slf4j.Slf4j;
@@ -13,6 +14,58 @@ import java.util.stream.Collectors;
  */
 @Slf4j
 public class Solution {
+
+    /**
+     * 2. 两数相加
+     * 给你两个<strong>非空</strong>的链表，表示两个非负的整数。它们每位数字都是按照<strong>逆序</strong>的方式存储的，并且每个节点只能存储<strong>一位</strong>数字。
+     * 请你将两个数相加，并以相同形式返回一个表示和的链表。
+     * 你可以假设除了数字<strong>0</strong>之外，这两个数都不会以<strong>0</strong>开头。
+     * @param l1 链表1
+     * @param l2 链表2
+     * @return 相加后的值
+     */
+    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
+        ListNode result = new ListNode(-1);
+        // 头指针
+        ListNode pointer = new ListNode(-1, result);
+        // l1、l2和的进位
+        int redundant = 0;
+        while (l1 != null && l2 != null) {
+            // 通过指针赋值
+            pointer.next.val = (l1.val + l2.val + redundant) % 10;
+            pointer.next.next = new ListNode(-1);
+            pointer.next = pointer.next.next;
+            redundant = (l1.val + l2.val + redundant)>9 ? (l1.val + l2.val + redundant) / 10 : 0;
+
+            // l1 l2 指针往后移一位
+            l1 = l1.next;
+            l2 = l2.next;
+        }
+        // 计算出将最后一位的值
+        int lastSum = (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val) + redundant;
+
+        // 最后一位如果有进位则新建一个节点
+        if (lastSum >= 10) {
+            pointer.next.val = lastSum % 10;
+            pointer.next.next = new ListNode(lastSum / 10);
+            pointer.next = pointer.next.next;
+        } else if (lastSum > 0){
+            pointer.next.val = lastSum;
+        }
+
+        // 判断result最后是否有空节点, 有的话去掉
+        pointer = result;
+        while (pointer != null) {
+            if (pointer.next != null && pointer.next.val == -1) {
+                pointer.next = null;
+                break;
+            }
+            pointer = pointer.next;
+        }
+
+        return result;
+    }
+
     /**
      * 212.单词搜索Ⅱ
      *      给定一个m x n 二维字符网格board和一个单词（字符串）列表 words，找出所有同时在二维网格和字典中出现的单词。
@@ -149,6 +202,57 @@ public class Solution {
         return collect.stream().min(Comparator.comparingInt(String::length)).orElse("");
     }
 
+    /**
+     * 807. 保持城市天际线<br/>
+     * 给你一座由 n x n 个街区组成的城市，每个街区都包含一座立方体建筑。给你一个下标从 0 开始的 n x n 整数矩阵 grid ，其中 grid[r][c] 表示坐落于 r 行 c 列的建筑物的 高度 。<br/>
+     * 城市的 天际线 是从远处观察城市时，所有建筑物形成的外部轮廓。从东、南、西、北四个主要方向观测到的 天际线 可能不同。<br/>
+     * 我们被允许为 任意数量的建筑物 的高度增加 任意增量（不同建筑物的增量可能不同） 。 高度为 0 的建筑物的高度也可以增加。然而，增加的建筑物高度 不能影响 从任何主要方向观察城市得到的 天际线 。<br/>
+     * 在 不改变 从任何主要方向观测到的城市 天际线 的前提下，返回建筑物可以增加的 最大高度增量总和 。<br/>
+     * @param grid 城市建筑矩阵
+     * @return 最高增量总和
+     */
+    public int maxIncreaseKeepingSkyline(int[][] grid) {
+        int[] colMax = new int[grid.length];
+        int[] rowMax = new int[grid.length];
+        int totalAdd = 0;
+
+        long startTime = System.currentTimeMillis();
+        // 先寻找行列的最大值
+        for (int outIndex=0; outIndex<grid.length; outIndex++) {
+
+            int[] tmp = grid[outIndex];
+
+            for (int inIndex=0; inIndex<tmp.length; inIndex++) {
+
+                if (colMax[outIndex] < tmp[inIndex]) {
+                    colMax[outIndex] = tmp[inIndex];
+                }
+
+                if (rowMax[inIndex] < tmp[inIndex]) {
+                    rowMax[inIndex] = tmp[inIndex];
+                }
+            }
+
+        }
+
+        for (int outIndex=0; outIndex<grid.length; outIndex++) {
+
+            for (int inIndex = 0; inIndex < grid[outIndex].length; inIndex++) {
+                int currItem = grid[outIndex][inIndex];
+                if (currItem < rowMax[inIndex] && currItem < colMax[outIndex]) {
+                    totalAdd += rowMax[inIndex] < colMax[outIndex]
+                            ? rowMax[inIndex] - currItem
+                            : colMax[outIndex] - currItem;
+                }
+
+            }
+
+        }
+
+        System.out.println(System.currentTimeMillis() - startTime + "ms");
+        return totalAdd;
+    }
+
     /**
      * 878. 第N个神奇数字
      *      如果正整数可以被 A 或 B 整除，那么它是神奇的。
diff --git a/src/main/java/cn/hy/test/SolutionTest.java b/src/main/java/cn/hy/test/SolutionTest.java
index ecda25e6d622cea72e62153ef5c8167007a3f2e9..9dbf05a5e63f4351239aaf06a2f789962aca002a 100644
--- a/src/main/java/cn/hy/test/SolutionTest.java
+++ b/src/main/java/cn/hy/test/SolutionTest.java
@@ -1,6 +1,10 @@
 package cn.hy.test;
 
+import cn.hy.entity.ListNode;
 import cn.hy.leetcode.Solution;
+import cn.hy.util.ListNodeConstructor;
+import org.junit.Test;
+
 import lombok.extern.slf4j.Slf4j;
 import org.junit.Test;
 
@@ -9,6 +13,23 @@ import java.util.*;
 @Slf4j
 public class SolutionTest {
     Solution solution = new Solution();
+
+    /**
+     * 2.两数相加
+     */
+    @Test
+    public void addTwoNumbers() {
+        ListNode l1 = ListNodeConstructor.ConstructListNode(5);
+        ListNode l2 = ListNodeConstructor.ConstructListNode(4);
+
+        ListNode result = solution.addTwoNumbers(l1, l1);
+
+        while (result.next != null) {
+            System.out.printf("%d", result.val);
+            result = result.next;
+        }
+    }
+
     /**
      * 212.单词搜索Ⅱ
      */
@@ -71,6 +92,30 @@ public class SolutionTest {
         log.info(solution.shortestCompletingWord(licensePlate, words));
     }
 
+    /**
+     * 807. 保持城市天际线
+     */
+    @Test
+    public void testMaxIncreaseKeepingSkyline() {
+        // 动态生成grid测试用例
+//        int gridSize = 50;
+//        int[][] grid = new int[gridSize][gridSize];
+//        for (int out=0; out<gridSize; out++) {
+//            for (int in=0; in<gridSize; in++) {
+//                grid[out][in] = (int) Math.floor(Math.random() * 10);
+//            }
+//        }
+
+        // 手动输入grid测试用例
+//        int[][] grid ={{3, 0, 8, 4},
+//                        {2, 4, 5, 7},
+//                        {9, 2, 6, 3},
+//                        {0, 3, 1, 0}};
+        int[][] grid = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}};
+
+        System.out.println(solution.maxIncreaseKeepingSkyline(grid));
+    }
+
     /**
      * 878.第N个神奇数字
      */
diff --git a/src/main/java/cn/hy/util/ListNodeConstructor.java b/src/main/java/cn/hy/util/ListNodeConstructor.java
new file mode 100644
index 0000000000000000000000000000000000000000..fa33975a63bf298e980adb34b5869ba4971a70a8
--- /dev/null
+++ b/src/main/java/cn/hy/util/ListNodeConstructor.java
@@ -0,0 +1,31 @@
+package cn.hy.util;
+
+import cn.hy.entity.ListNode;
+
+import java.util.Random;
+
+public class ListNodeConstructor {
+    /**
+     * 返回一个指定长度的随机链表
+     * @return
+     */
+    public static ListNode ConstructListNode(int length) {
+        ListNode result = new ListNode(-1);
+        ListNode pointer = new ListNode(-1, result);
+        Random random;
+
+        while (length > 0) {
+            random = new Random(System.currentTimeMillis() + length);
+            pointer.next.val = random.nextInt(10);
+
+            if (length > 1){
+                pointer.next.next = new ListNode(-1);
+                pointer.next = pointer.next.next;
+            } else if (pointer.next.val == 0){
+                pointer.next.val = random.nextInt(9) + 1;
+            }
+            length--;
+        }
+        return result;
+    }
+}