diff --git a/Cargo.lock b/Cargo.lock
index 191f843e..ea91aec0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -295,10 +295,6 @@ dependencies = [
  "wasm-bindgen",
 ]
 
-[[package]]
-name = "leetcode"
-version = "0.1.0"
-
 [[package]]
 name = "libc"
 version = "0.2.147"
@@ -557,6 +553,10 @@ dependencies = [
  "serde_json",
 ]
 
+[[package]]
+name = "two_sum"
+version = "0.1.0"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.11"
diff --git a/Cargo.toml b/Cargo.toml
index fa613706..9b8dbe23 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,7 +10,7 @@ members = [
   "electronics",
   "financial",
   "geodesy",
-  "leetcode",
+  "leetcode/*.*",
   "math",
   "physics",
   "weiss/c02",
diff --git a/leetcode/Cargo.toml b/leetcode/001.two_sum/Cargo.toml
similarity index 64%
rename from leetcode/Cargo.toml
rename to leetcode/001.two_sum/Cargo.toml
index 474153f5..a94a8b4d 100644
--- a/leetcode/Cargo.toml
+++ b/leetcode/001.two_sum/Cargo.toml
@@ -1,7 +1,6 @@
 [package]
-name = "leetcode"
+name = "two_sum"
 version = "0.1.0"
 edition = "2021"
-publish = false
 
 [dependencies]
diff --git a/leetcode/src/bin/l01_two_sum.rs b/leetcode/001.two_sum/src/main.rs
similarity index 70%
rename from leetcode/src/bin/l01_two_sum.rs
rename to leetcode/001.two_sum/src/main.rs
index f6f624af..390a8b12 100644
--- a/leetcode/src/bin/l01_two_sum.rs
+++ b/leetcode/001.two_sum/src/main.rs
@@ -7,7 +7,7 @@
 fn solution1(nums: &[i32], target: i32) -> Option<(usize, usize)> {
     for (i, m) in nums.iter().enumerate() {
         for (j, n) in nums.iter().enumerate() {
-            if m + n == target {
+            if i != j && m + n == target {
                 return Some((i, j));
             }
         }
@@ -19,4 +19,12 @@ fn main() {
     let nums = &[2, 7, 11, 15];
     let target = 9;
     assert_eq!(solution1(nums, target), Some((0, 1)));
+
+    let nums = &[3, 2, 4];
+    let target = 6;
+    assert_eq!(solution1(nums, target), Some((1, 2)));
+
+    let nums = &[3, 3];
+    let target = 6;
+    assert_eq!(solution1(nums, target), Some((0, 1)));
 }
diff --git a/leetcode/src/bin/l02_add_two_numbers.rs b/leetcode/src/bin/l02_add_two_numbers.rs
new file mode 100644
index 00000000..3eec9925
--- /dev/null
+++ b/leetcode/src/bin/l02_add_two_numbers.rs
@@ -0,0 +1,83 @@
+// Copyright (c) 2023 Xu Shaohua <shaohua@biofan.org>. All rights reserved.
+// Use of this source is governed by General Public License that can be
+// found in the LICENSE file.
+
+//! Problem: [Add two numbers](https://leetcode.com/problems/add-two-numbers)
+
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+pub struct ListNode {
+    pub val: i32,
+    pub next: ListNodePtr,
+}
+
+pub type ListNodePtr = Option<Box<ListNode>>;
+
+impl ListNode {
+    #[must_use]
+    #[inline]
+    pub fn new(val: i32) -> Self {
+        Self { val, next: None }
+    }
+
+    #[must_use]
+    #[inline]
+    pub fn new_ptr(val: i32) -> ListNodePtr {
+        Some(Box::new(Self::new(val)))
+    }
+
+    pub fn push_head(head: ListNodePtr, val: i32) -> ListNodePtr {
+        Some(Box::new(Self { val, next: head }))
+    }
+
+    pub fn push_tail(tail: &mut ListNodePtr, val: i32) -> ListNodePtr {
+        debug_assert!(tail.next.is_none());
+        let new_tail = Self::new_ptr(val);
+        tail.next = new_tail;
+        new_tail
+    }
+
+    #[must_use]
+    pub fn from_slice(s: &[i32]) -> ListNodePtr {
+        assert!(s.len() > 0);
+        let mut list = None;
+        for val in s.iter().rev() {
+            list = Self::push_head(list, *val);
+        }
+        list
+    }
+}
+
+fn solution1(l1: ListNodePtr, l2: ListNodePtr) -> ListNodePtr {
+    let mut l3 = None;
+    let div = 0;
+    let rem = 0;
+    loop {
+        l1 = l1.unwrap();
+        l2 = l2.unwrap();
+        let val1 = l1.value;
+        l1 = l1.next();
+        let val2 = l2.value;
+        l2 = l2.next();
+        (div, rem) = (l1 + l2 + div).div_rem(10);
+        l3 = ListNode::push_head(l3, rem);
+
+        if l1.is_none() {
+            l2.value += div;
+            l3.next = l2;
+            break;
+        }
+        if l2.is_none() {
+            l1.value += div;
+            l3.next = l1;
+            break;
+        }
+    }
+    l3
+}
+
+fn main() {
+    let l1 = ListNode::from_slice(&[2, 4, 3]);
+    let l2 = ListNode::from_slice(&[5, 6, 4]);
+    let target = ListNode::from_slice(&[7, 0, 8]);
+    assert_eq!(solution1(l1, l2), target);
+}
diff --git a/weiss/CMakeLists.txt b/weiss/CMakeLists.txt
index 8cb0b239..a9713514 100644
--- a/weiss/CMakeLists.txt
+++ b/weiss/CMakeLists.txt
@@ -3,3 +3,4 @@ cmake_minimum_required(VERSION 3.10)
 project(weiss C)
 
 add_subdirectory(c03)
+add_subdirectory(c07)
diff --git a/weiss/c07/CMakeLists.txt b/weiss/c07/CMakeLists.txt
new file mode 100644
index 00000000..e69de29b