From c56dc80737d763335c5dbc2258df8a85982d3ba8 Mon Sep 17 00:00:00 2001
From: begeekmyfriend <begeekmyfriend@gmail.com>
Date: Mon, 17 Jul 2017 16:06:05 +0800
Subject: [PATCH] Swap nodes in pairs

Signed-off-by: begeekmyfriend <begeekmyfriend@gmail.com>
---
 024_swap_nodes_in_pairs/Makefile     |  2 +
 024_swap_nodes_in_pairs/swap_nodes.c | 56 ++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)
 create mode 100644 024_swap_nodes_in_pairs/Makefile
 create mode 100644 024_swap_nodes_in_pairs/swap_nodes.c

diff --git a/024_swap_nodes_in_pairs/Makefile b/024_swap_nodes_in_pairs/Makefile
new file mode 100644
index 0000000..a3f3513
--- /dev/null
+++ b/024_swap_nodes_in_pairs/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test swap_nodes.c
diff --git a/024_swap_nodes_in_pairs/swap_nodes.c b/024_swap_nodes_in_pairs/swap_nodes.c
new file mode 100644
index 0000000..c491b22
--- /dev/null
+++ b/024_swap_nodes_in_pairs/swap_nodes.c
@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+struct ListNode {
+    int val;
+    struct ListNode *next;
+};
+
+static struct ListNode* swapPairs(struct ListNode* head) {
+    struct ListNode dummy, *p, *prev, *next;
+    if (head == NULL) {
+        return NULL;
+    }
+    dummy.next = head;
+    prev = &dummy;
+    p = dummy.next;
+    next = p->next;
+    while (p != NULL && next != NULL) {
+        prev->next = next;
+        p->next = next->next;
+        next->next = p;
+        prev = p;
+        p = p->next;
+        if (p != NULL) {
+           next = p->next;
+        }
+    }
+    return dummy.next;
+}
+
+int main(int argc, char **argv)
+{
+    int i;
+    struct ListNode *p, *prev, dummy, *list;
+
+    dummy.next = NULL;
+    prev = &dummy;
+    for (i = 1; i < argc; i++) {
+        p = malloc(sizeof(*p));
+        int n = atoi(argv[i]);
+        printf("%d ", n);
+        p->val = n;
+        p->next = NULL;
+        prev->next = p;
+        prev = p;
+    }
+    putchar('\n');
+
+    list = swapPairs(dummy.next);
+    for (p = list; p != NULL; p = p->next) {
+        printf("%d ", p->val);
+    }
+    putchar('\n');
+
+    return 0;
+}