diff --git a/algorithm_interview_course/chapter_two/section_2.cpp b/algorithm_interview_course/chapter_two/section_2.cpp
new file mode 100644
index 00000000..39a74475
--- /dev/null
+++ b/algorithm_interview_course/chapter_two/section_2.cpp
@@ -0,0 +1,65 @@
+/* ************************************************************************
+> File Name:     algorithm_2.cpp
+> Author:        sunxiuyang
+> Mail:          sunxiuyang04@gmail.com 
+> Created Time:  Thu Jan 30 16:09:35 2020
+> Description:   
+ ************************************************************************/
+
+#include <iostream>
+#include <chrono>
+#include <thread>
+using namespace std;
+using namespace chrono;
+
+// O(n)
+void function1(long long n) {
+    long long k = 0;
+    for (long long i = 0; i < n; i++) {
+        k++;
+    }
+}
+
+// O(n^2)
+void function2(long long n) {
+    long long k = 0;
+    for (long long i = 0; i < n; i++) {
+        for (long j = 0; j < n; j++) {
+            k++;
+        }
+    }
+
+}
+
+// O(nlogn)
+void function3(long long n) {
+    long long k = 0;
+    for (long long i = 0; i < n; i++) {
+        for (long long j = 1; j < n; j = j*2) { // 注意这里j=1
+            k++;
+        }
+    }
+}
+
+
+void time_test() {
+    long long n; // 数据规模
+    while (cin>>n) {
+        milliseconds start_time = duration_cast<milliseconds >(
+            system_clock::now().time_since_epoch()
+        );
+
+        function3(n);
+
+        milliseconds end_time = duration_cast<milliseconds >(
+            system_clock::now().time_since_epoch()
+        );
+        cout << milliseconds(end_time).count() - milliseconds(start_time).count() 
+            <<" ms"<< endl;
+    }
+}
+
+int main() {
+    time_test();
+}
+
diff --git a/algorithm_interview_course/chapter_two/section_3.cpp b/algorithm_interview_course/chapter_two/section_3.cpp
new file mode 100644
index 00000000..77e9f9fc
--- /dev/null
+++ b/algorithm_interview_course/chapter_two/section_3.cpp
@@ -0,0 +1,55 @@
+/* ************************************************************************
+> File Name:     section_3.cpp
+> Author:        sunxiuyang
+> Mail:          sunxiuyang04@gmail.com 
+> Created Time:  Sat Feb  8 22:00:32 2020
+> Description:   
+ ************************************************************************/
+
+#include<iostream>
+using namespace std;
+
+int function1(int x, int n) {
+    int result = 1;  // 注意 任何数的0次方等于1 
+    for (int i = 0; i < n; i++) {
+        result = result * x;
+    }
+    return result;
+}
+
+int function2(int x, int n) {
+    if (n == 0) {
+        return 1; // return 1 同样是因为0次方是等于1的
+    }
+    return function2(x, n - 1) * x;
+}
+
+int function3(int x, int n) {
+    if (n == 0) {
+        return 1;
+    }
+    // if (n == 1) { // 这里如果不作处理就会陷入死循环
+    //     return x;
+    // }
+    if (n % 2 == 1) {
+        return function3(x, n/2) * function3(x, n/2) * x;
+    } 
+    return function3(x, n/2) * function3(x, n/2);
+}
+
+int function4(int x, int n) {
+    if (n == 0) {
+        return 1;
+    }
+    int t = function4(x, n/2);
+    if (n % 2 == 1) {
+        return t*t*x;
+    } 
+    return t*t;
+}
+int main() {
+    int x, n;
+    while (cin >> x >> n) {
+        cout << function3(x, n) << endl;
+    }
+}
diff --git a/algorithm_interview_course/chapter_two/section_4.cpp b/algorithm_interview_course/chapter_two/section_4.cpp
new file mode 100644
index 00000000..84ddd192
--- /dev/null
+++ b/algorithm_interview_course/chapter_two/section_4.cpp
@@ -0,0 +1,25 @@
+/* ************************************************************************
+> File Name:     section_4.cpp
+> Author:        sunxiuyang
+> Mail:          sunxiuyang04@gmail.com 
+> Created Time:  Tue Feb 18 23:34:08 2020
+> Description:   
+ ************************************************************************/
+
+#include<iostream> 
+using namespace std;
+
+struct node{
+   int num;
+   char cha;
+}st;
+
+int main() {
+    int a[100];
+    char b[100];
+    cout << sizeof(int) << endl;
+    cout << sizeof(char) << endl;
+    cout << sizeof(a) << endl;
+    cout << sizeof(b) << endl;
+    cout << sizeof(st) << endl;
+}
diff --git a/algorithm_interview_course/chapter_two/section_5.cpp b/algorithm_interview_course/chapter_two/section_5.cpp
new file mode 100644
index 00000000..1c6415b6
--- /dev/null
+++ b/algorithm_interview_course/chapter_two/section_5.cpp
@@ -0,0 +1,104 @@
+/* ************************************************************************
+> File Name:     section_5.cpp
+> Author:        sunxiuyang
+> Mail:          sunxiuyang04@gmail.com 
+> Created Time:  Mon Feb 24 18:44:56 2020
+> Description:   
+ ************************************************************************/
+
+#include <iostream>
+#include <chrono>
+#include <thread>
+using namespace std;
+using namespace chrono;
+
+int fibonacci_1(int n) {
+    if (n <= 0) {
+        return 0;
+    }
+    if (n == 1 || n == 2) {
+        return 1;
+    }
+    int first = 1, second = 1; 
+    int sum = first + second; 
+    for (int i = 2; i < n; i++) {
+        sum = first + second;
+        first = second;
+        second = sum;
+    }
+    return sum;
+}
+
+
+int fibonacci_2(int i) {
+       if(i <= 0) return 0;
+       if(i == 1) return 1;
+       return fibonacci_2(i - 1) + fibonacci_2(i - 2);
+}
+
+int fibonacci_3(int first, int second, int n) {
+    if (n <= 0) {
+        return 0;
+    }
+    if (n < 3) {
+        return 1;
+    }
+    else if (n == 3) {
+        return first + second;
+    }
+    else {
+        return fibonacci_3(second, first + second, n - 1);
+    }
+}
+
+
+void test_fibonacci() {
+    int n;
+    while(cin >> n) {
+        cout << fibonacci_1(n) << endl;
+        cout << fibonacci_2(n) << endl;
+        cout << fibonacci_3(1, 1, n) << endl;
+    } 
+}
+
+int binary_search(int arr[], int l, int r, int n) {
+    if (r >= l) {
+        int mid = l + (r - l) / 2;
+        if (arr[mid] == n)
+            return mid;
+        if (arr[mid] > n)
+            return binary_search(arr, l, mid - 1, n);
+        return binary_search(arr, mid + 1, r, n);
+    }
+    return -1;
+}
+int arr[] = {2, 3, 4, 5, 8, 10, 15, 17, 20};
+int binary_search(int l, int r, int n) {
+    if (r >= l) {
+        int mid = l + (r - l) / 2;
+        if (arr[mid] == n)
+            return mid;
+        if (arr[mid] > n)
+            return binary_search(l, mid - 1, n);
+        return binary_search(mid + 1, r, n);
+    }
+    return -1;
+}
+
+void test_binary_search(void) {
+    int arr[] = {2, 3, 4, 5, 8, 10, 15, 17, 20};
+    int x = 17;
+    int n = sizeof(arr) / sizeof(arr[0]);
+    // int result = binary_search(arr, 0, n - 1, x);
+    int result = binary_search(0, n - 1, x);
+    (result == -1) ? cout << "Element is not present in array"
+                   : cout << "Element is present at index " << result;
+}
+
+int main()
+{
+    // test_binary_search();
+    // test_fibonacci();
+    return 0;
+}
+
diff --git a/algorithm_interview_course/chapter_two/section_6.cpp b/algorithm_interview_course/chapter_two/section_6.cpp
new file mode 100644
index 00000000..a63ae21d
--- /dev/null
+++ b/algorithm_interview_course/chapter_two/section_6.cpp
@@ -0,0 +1,33 @@
+
+#include <iostream>
+#include <chrono>
+#include <thread>
+using namespace std;
+using namespace chrono;
+int fibonacci_2(int i) {
+       if(i <= 0) return 0;
+       if(i == 1) return 1;
+       return fibonacci_2(i - 1) + fibonacci_2(i - 2);
+}
+void time_consumption() {
+    int n;
+    while (cin >> n) {
+        milliseconds start_time = duration_cast<milliseconds >(
+            system_clock::now().time_since_epoch()
+        );
+
+        fibonacci_2(n);
+
+        milliseconds end_time = duration_cast<milliseconds >(
+            system_clock::now().time_since_epoch()
+        );
+        cout << milliseconds(end_time).count() - milliseconds(start_time).count() 
+            <<" ms"<< endl;
+    }
+}
+int main()
+{
+    time_consumption();
+    return 0;
+}
+
diff --git a/problems/0000.TwoSum.md b/problems/0000.TwoSum.md
new file mode 100644
index 00000000..c3b7e31d
--- /dev/null
+++ b/problems/0000.TwoSum.md
@@ -0,0 +1,70 @@
+## 题目地址 
+https://leetcode-cn.com/problems/two-sum/ 
+
+## 思路 
+
+## 一般解法 
+
+代码：
+
+```C++
+```
+
+## 优化解法 
+
+```C++
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        for (int i = 0; i < nums.size(); i ++) {
+            for (int j = i + 1; j < nums.size(); j++) {
+                if (nums[i] + nums[j] == target) {
+                    return {i, j};
+                }
+            }
+        }
+        return {};
+    }
+};
+
+```
+
+```
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        std::map <int,int> map;
+        for(int i = 0; i < nums.size(); i++) {
+            auto iter = map.find(target - nums[i]);
+            if(iter != map.end()) {
+                return {iter->second,i};
+            }
+            map[nums[i]] = i;
+        }
+        return {};
+    }
+};
+```
+
+```
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        std::unordered_map <int,int> map;
+        for(int i = 0; i < nums.size(); i++) {
+            auto iter = map.find(target - nums[i]);
+            if(iter != map.end()) {
+                return {iter->second, i};
+                break;
+            }
+            map.emplace(nums[i], i);
+        }
+        return {};
+    }
+};
+```
+## 代码
+
+```C++
+
+```