Add two numbers

Signed-off-by: begeekmyfriend <[email protected]>

2_add_two_numbers/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test add_two_numbers.c

2_add_two_numbers/add_two_numbers.c

@@ -0,0 +1,100 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* Definition for singly-linked list. */
+struct ListNode {
+    int val;
+    struct ListNode *next;
+};
+
+struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
+    int carry_num = 0;
+    int first = 1;
+    struct ListNode *res = NULL;
+    struct ListNode *p = NULL;
+    struct ListNode *prev = p;
+
+    while (l1 != NULL || l2 != NULL || carry_num) {
+        int sum = 0;
+        int last_carry = carry_num;
+        if (l1 != NULL) {
+            sum += l1->val;
+            l1 = l1->next;
+        }
+        if (l2 != NULL) {
+            sum += l2->val;
+            l2 = l2->next;
+        }
+        if (sum >= 10) {
+            sum -= 10;
+            carry_num = 1;
+        } else {
+            carry_num = 0;
+        }
+
+        p = malloc(sizeof(*p));
+        if (first) {
+             res = p;
+             first = 0;
+        }
+        p->val = sum + last_carry;
+        if (p->val >= 10) {
+            p->val -= 10;
+            carry_num = 1;
+        }
+        p->next = NULL;
+        if (prev != NULL) {
+             prev->next = p;
+        }
+        prev = p;
+    }
+
+    return res;
+}
+
+static struct ListNode *node_build(const char *digits)
+{
+    struct ListNode *res, *p, *prev;
+    int first = 1;
+    int len = strlen(digits);
+    const char *c = digits + len - 1;
+    prev = NULL;
+    while (len-- > 0) {
+        p = malloc(sizeof(*p));
+        if (first) {
+            first = 0;
+            res = p;
+        }
+        p->val = *c-- - '0';
+        p->next = NULL;
+        if (prev != NULL) {
+            prev->next = p;
+        }
+        prev = p;
+    }
+
+    return res;
+}
+
+static void show(struct ListNode *ln)
+{
+    int sum = 0, factor = 1;
+    while (ln != NULL) {
+        sum += ln->val * factor;
+        factor *= 10;
+        ln = ln->next;
+    }
+    printf("%d\n", sum);
+}
+
+int main(int argc, char **argv)
+{
+    struct ListNode *l1 = node_build(argv[1]);
+    struct ListNode *l2 = node_build(argv[2]);
+    struct ListNode *res = addTwoNumbers(l1, l2);
+    show(l1);
+    show(l2);
+    show(res);
+    return 0;
+}