From 42d4fb57415a05f20d3b1c4c4b786465a8276e63 Mon Sep 17 00:00:00 2001
From: Shubham Patil <shubhampatil.patil@gmail.com>
Date: Sat, 5 Oct 2019 19:17:38 +0530
Subject: [PATCH 1/7] Solution for "2. Add Two Numbers"

---
 leetcode/README.md |  3 ++-
 leetcode/src/2.c   | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 leetcode/src/2.c

diff --git a/leetcode/README.md b/leetcode/README.md
index 1718af9ddd..36138a8cd4 100644
--- a/leetcode/README.md
+++ b/leetcode/README.md
@@ -7,6 +7,7 @@ LeetCode
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
 |1|[Two Sum](https://https://leetcode.com/problems/two-sum/) | [C](./src/1.c)|Easy
+|2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | [C](./src/2.c)|Medium|
 |3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [C](./src/3.c)|Medium|
 |20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/) | [C](./src/20.c)|Easy|
 |24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [C](./src/24.c)|Medium|
@@ -66,4 +67,4 @@ LeetCode
 |938|[Range Sum of BST](https://leetcode.com/problems/range-sum-of-bst/) | [C](./src/938.c)|Easy|
 |965|[Univalued Binary Tree](https://leetcode.com/problems/univalued-binary-tree/) | [C](./src/965.c)|Easy|
 |977|[Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/) | [C](./src/977.c)|Easy|
-|1189|[Maximum Number of Balloons](https://leetcode.com/problems/maximum-number-of-balloons/) | [C](./src/1189.c)|Easy|
\ No newline at end of file
+|1189|[Maximum Number of Balloons](https://leetcode.com/problems/maximum-number-of-balloons/) | [C](./src/1189.c)|Easy|
diff --git a/leetcode/src/2.c b/leetcode/src/2.c
new file mode 100644
index 0000000000..1336f339f8
--- /dev/null
+++ b/leetcode/src/2.c
@@ -0,0 +1,43 @@
+struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
+    struct ListNode *head = NULL;
+    struct ListNode *walk = NULL;
+    struct ListNode *tmp = NULL;
+
+    int carry = 0;
+    int val1 = 0;
+    int val2 = 0;
+    int val = 0;
+
+    while(l1 != NULL || l2 != NULL || carry) {
+        val1 = 0;
+        val2 = 0;
+        val = 0;
+
+        if(l1) {
+            val1 = l1->val;
+            l1 = l1->next;
+        }
+
+        if(l2) {
+            val2 = l2->val;
+            l2 = l2->next;
+        }
+
+        val = carry + val1 + val2;
+        carry = val / 10;
+
+        tmp = malloc(sizeof(struct ListNode));
+        tmp->val = val % 10;
+        tmp->next = NULL;
+
+        if(!head) {
+            head = walk = tmp;
+        } else {
+            walk->next = tmp;
+            walk = walk->next;
+        }
+    }
+
+    return head;
+}
+

From 4d11bc02227b747d3098bbc35b4d15c52ae2d3bd Mon Sep 17 00:00:00 2001
From: Shubham Patil <shubhampatil.patil@gmail.com>
Date: Sat, 5 Oct 2019 19:19:12 +0530
Subject: [PATCH 2/7] Solution for "4. Median of Two Sorted Arrays"

---
 leetcode/README.md |  1 +
 leetcode/src/4.c   | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 leetcode/src/4.c

diff --git a/leetcode/README.md b/leetcode/README.md
index 36138a8cd4..4063f3213f 100644
--- a/leetcode/README.md
+++ b/leetcode/README.md
@@ -9,6 +9,7 @@ LeetCode
 |1|[Two Sum](https://https://leetcode.com/problems/two-sum/) | [C](./src/1.c)|Easy
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | [C](./src/2.c)|Medium|
 |3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [C](./src/3.c)|Medium|
+|4|[Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/) | [C](./src/4.c)|Hard|
 |20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/) | [C](./src/20.c)|Easy|
 |24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [C](./src/24.c)|Medium|
 |26|[Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) | [C](./src/26.c)|Easy|
diff --git a/leetcode/src/4.c b/leetcode/src/4.c
new file mode 100644
index 0000000000..1ac71c4b52
--- /dev/null
+++ b/leetcode/src/4.c
@@ -0,0 +1,29 @@
+double findMedianSortedArrays(int* nums1, int nums1Size, int* nums2, int nums2Size) {
+    int i = 0;
+    int j = 0;
+    int k = 0;
+    int mid = 0;
+    int len = nums1Size + nums2Size;
+    int arr[len];
+    
+    while(i < nums1Size && j < nums2Size) {
+        if(nums1[i] > nums2[j])
+            arr[k++] = nums2[j++];
+        else 
+            arr[k++] = nums1[i++];
+    }
+    
+    while(i < nums1Size)
+        arr[k++] = nums1[i++];
+    
+    while(j < nums2Size)
+        arr[k++] = nums2[j++];
+    
+    mid = len / 2;
+    if (len % 2 == 1)
+        return (int)arr[mid];
+    else 
+        return (arr[mid - 1] + arr[mid]) / 2.0;
+    
+}
+

From 439ef79f26c9aa264dce9587096cff34005e4150 Mon Sep 17 00:00:00 2001
From: Shubham Patil <shubhampatil.patil@gmail.com>
Date: Sat, 5 Oct 2019 19:20:01 +0530
Subject: [PATCH 3/7] Solution for "7. Reverse Integer"

---
 leetcode/README.md |  1 +
 leetcode/src/7.c   | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)
 create mode 100644 leetcode/src/7.c

diff --git a/leetcode/README.md b/leetcode/README.md
index 4063f3213f..22fb09cd12 100644
--- a/leetcode/README.md
+++ b/leetcode/README.md
@@ -10,6 +10,7 @@ LeetCode
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | [C](./src/2.c)|Medium|
 |3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [C](./src/3.c)|Medium|
 |4|[Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/) | [C](./src/4.c)|Hard|
+|7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/) | [C](.src/7.c)|Easy|
 |20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/) | [C](./src/20.c)|Easy|
 |24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [C](./src/24.c)|Medium|
 |26|[Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) | [C](./src/26.c)|Easy|
diff --git a/leetcode/src/7.c b/leetcode/src/7.c
new file mode 100644
index 0000000000..9984dcc95d
--- /dev/null
+++ b/leetcode/src/7.c
@@ -0,0 +1,17 @@
+int reverse(int x) {
+    int dig = 0;
+    int num = 0;
+    
+     while(x != 0) {
+        dig = x %  10;
+        x /= 10;
+        
+        if(num > INT_MAX / 10 || num == INT_MAX / 10 && dig > 7) return 0;
+        if(num < INT_MIN / 10 || num == INT_MIN / 10 && dig < -8) return 0;
+        
+        num = (num * 10) + dig;
+    }
+
+    return num;
+}
+

From 33f2893592810adfc5331c4e490e1bd034666beb Mon Sep 17 00:00:00 2001
From: Shubham Patil <shubhampatil.patil@gmail.com>
Date: Sat, 5 Oct 2019 19:22:10 +0530
Subject: [PATCH 4/7] Solution for "8. String to Integer (atoi)"

---
 leetcode/README.md |  1 +
 leetcode/src/8.c   | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)
 create mode 100644 leetcode/src/8.c

diff --git a/leetcode/README.md b/leetcode/README.md
index 22fb09cd12..2254b248c0 100644
--- a/leetcode/README.md
+++ b/leetcode/README.md
@@ -11,6 +11,7 @@ LeetCode
 |3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [C](./src/3.c)|Medium|
 |4|[Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/) | [C](./src/4.c)|Hard|
 |7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/) | [C](.src/7.c)|Easy|
+|8|[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/) | [C](./src/8.c) |Medium|
 |20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/) | [C](./src/20.c)|Easy|
 |24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [C](./src/24.c)|Medium|
 |26|[Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) | [C](./src/26.c)|Easy|
diff --git a/leetcode/src/8.c b/leetcode/src/8.c
new file mode 100644
index 0000000000..4dd2f0f45b
--- /dev/null
+++ b/leetcode/src/8.c
@@ -0,0 +1,32 @@
+int myAtoi(char* str) {
+    int val = 0;
+    int i = 0;
+    int len = 0;
+    int dig = 0;
+    int neg_flag = 0;
+    
+    len = strlen(str);
+    if(!len)
+        return val;
+    
+    /* Get rid of whitespaces */
+    for(i = 0; i < len && str[i] == ' '; i++);
+    
+    if(str[i] == '-') {
+        neg_flag = 1;
+        i++;
+    } else if(str[i] == '+') {
+        i++;
+    }
+    
+    for(; str[i] >= '0' && str[i] <= '9'; i++) {
+        dig = str[i] - '0';
+        if(val > INT_MAX / 10 || val == INT_MAX / 10 && dig > 7)
+            return neg_flag ? INT_MIN : INT_MAX;
+        
+        val = (val * 10) + dig;
+    }
+    
+    return neg_flag ? (-1 * val) : val;
+}
+

From d2523614cef8a72a87eac3660459a620b7857732 Mon Sep 17 00:00:00 2001
From: Shubham Patil <shubhampatil.patil@gmail.com>
Date: Sat, 5 Oct 2019 19:23:57 +0530
Subject: [PATCH 5/7] Soulution for "21. Merge Two Sorted Lists"

---
 leetcode/README.md |  1 +
 leetcode/src/21.c  | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 leetcode/src/21.c

diff --git a/leetcode/README.md b/leetcode/README.md
index 2254b248c0..7c54d02e14 100644
--- a/leetcode/README.md
+++ b/leetcode/README.md
@@ -13,6 +13,7 @@ LeetCode
 |7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/) | [C](.src/7.c)|Easy|
 |8|[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/) | [C](./src/8.c) |Medium|
 |20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/) | [C](./src/20.c)|Easy|
+|21|[Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/) | [C](./src/21.c)|Easy|
 |24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [C](./src/24.c)|Medium|
 |26|[Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) | [C](./src/26.c)|Easy|
 |27|[Remove Element](https://leetcode.com/problems/remove-element/) | [C](./src/27.c)|Easy|
diff --git a/leetcode/src/21.c b/leetcode/src/21.c
new file mode 100644
index 0000000000..8c0a9308fa
--- /dev/null
+++ b/leetcode/src/21.c
@@ -0,0 +1,40 @@
+struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
+    struct ListNode *list = NULL;
+    struct ListNode *tmp = NULL;
+    
+    if (!l1)
+        return l2;
+    if (!l2)
+        return l1;
+    
+    if (l1 && l2) {
+        if (l1->val < l2->val) {
+            list = tmp = l1;
+            l1 = l1->next;
+        } else {
+            list = tmp = l2;
+            l2 = l2->next;
+        }
+        
+        while(l1 && l2) {
+            if (l1->val < l2->val) {
+                tmp->next = l1;
+                l1 = l1->next;
+            } else {
+                tmp->next = l2;
+                l2 = l2->next;
+            }
+            tmp = tmp->next;
+        }
+        
+        if (l1)
+            tmp->next = l1;
+        if (l2)
+            tmp->next = l2;
+        
+        return list;
+    }
+    
+    return NULL;
+}
+

From 082f9c8195c542504544b06449af8fc8ffa42dee Mon Sep 17 00:00:00 2001
From: Shubham Patil <shubhampatil.patil@gmail.com>
Date: Sat, 5 Oct 2019 19:25:08 +0530
Subject: [PATCH 6/7] Solution for "28. Implement strStr()"

---
 leetcode/README.md |  1 +
 leetcode/src/28.c  | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 leetcode/src/28.c

diff --git a/leetcode/README.md b/leetcode/README.md
index 7c54d02e14..375d866868 100644
--- a/leetcode/README.md
+++ b/leetcode/README.md
@@ -17,6 +17,7 @@ LeetCode
 |24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [C](./src/24.c)|Medium|
 |26|[Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) | [C](./src/26.c)|Easy|
 |27|[Remove Element](https://leetcode.com/problems/remove-element/) | [C](./src/27.c)|Easy|
+|28|[Implement strStr()](https://leetcode.com/problems/implement-strstr/) | [C](./src/28.c)|Easy|
 |35|[Search Insert Position](https://leetcode.com/problems/search-insert-position/) | [C](./src/35.c)|Easy|
 |53|[Maximum Subarray](https://leetcode.com/problems/maximum-subarray/) | [C](./src/53.c)|Easy|
 |82|[Remove Duplicates from Sorted List II](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/) | [C](./src/82.c)|Medium|
diff --git a/leetcode/src/28.c b/leetcode/src/28.c
new file mode 100644
index 0000000000..1f019718cd
--- /dev/null
+++ b/leetcode/src/28.c
@@ -0,0 +1,37 @@
+int strStr(char* haystack, char* needle) {
+    int i = 0;
+    int j = 0;
+    int k = 0;
+    int hlen = 0;
+    int nlen = 0;
+    
+    if(needle == NULL || *needle == 0)
+        return 0;
+    
+    if(haystack == NULL || *haystack == 0)
+        return -1;
+    
+    hlen = strlen(haystack);
+    nlen = strlen(needle);
+    
+    if(hlen < nlen)
+        return -1;
+    
+    for(i = 0; i <= hlen - nlen; i++) {  
+        j = 0;
+        if(haystack[i] != needle[j++])
+            continue;
+        
+        k = i + 1;
+        for(; j < nlen; j++) {
+            if(haystack[k] != needle[j]) {
+                break;
+            } else
+                k++;
+        }
+        if(j == nlen)
+            return i;
+    }
+    return -1;
+}
+

From 58a77bdc50e9e6fb4dac68ef3674df9932a7f74d Mon Sep 17 00:00:00 2001
From: Shubham Patil <shubhampatil.patil@gmail.com>
Date: Mon, 7 Oct 2019 08:07:52 +0530
Subject: [PATCH 7/7] Adding recusrsive approach to "21. Merge Two Sorted
 Lists"

---
 leetcode/src/21.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/leetcode/src/21.c b/leetcode/src/21.c
index 8c0a9308fa..5d9d0e7caa 100644
--- a/leetcode/src/21.c
+++ b/leetcode/src/21.c
@@ -1,3 +1,4 @@
+/* Iterative approach */
 struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
     struct ListNode *list = NULL;
     struct ListNode *tmp = NULL;
@@ -38,3 +39,18 @@ struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
     return NULL;
 }
 
+
+/* Recursive approach */
+struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
+    if(!l1)
+        return l2;t 
+        return l1;
+    if(l1->val < l2->val) {
+        l1->next = mergeTwoLists(l1->next, l2);
+        return l1;
+    } else {
+        l2->next = mergeTwoLists(l1, l2->next);
+        return l2;
+    }
+}
+