two pointers is not that easy

Author: Ainevsia

86. Partition List/Solution.cpp

@@ -0,0 +1,63 @@
+#include <string>
+#include <vector>
+#include <iostream>
+#include <sstream>
+#include <algorithm>
+using namespace std;
+
+// Definition for singly-linked list.
+struct ListNode {
+    int val;
+    ListNode *next;
+    ListNode(int x) : val(x), next(NULL) {}
+};
+
+class Solution {
+public:
+    ListNode* partition(ListNode* head, int x) {
+        if (head == NULL) return head;
+        ListNode * header = new ListNode(0);
+        header->next = head;
+        auto p1 = header, p2 = header;  // p1, p2 not NULL
+        // p1 -> the last number < x, p2 -> cur
+        while (p2 != NULL and p2->next != NULL) {    // see the next node value
+            if (p2->next->val < x) {
+                if ( p1 == p2 ) {
+                    p1 = p1->next;
+                    p2 = p2->next;
+                    continue;
+                }
+                // swap 
+                auto p3 = p2->next, p4 = p3->next;
+                auto p1n = p1->next;
+                p1->next = p3;
+                p3->next = p1n;
+                p2->next = p4;
+                p1 = p1->next;
+            } else 
+                p2 = p2->next;
+        }
+        return header->next;
+    }
+};
+
+int main() {
+    Solution s;
+    ListNode a(1);
+    ListNode b(4);
+    ListNode c(3);
+    ListNode d(2);
+    ListNode e(5);
+    ListNode f(2);
+    a.next = &b;
+    b.next = &c;
+    c.next = &d;
+    d.next = &e;
+    e.next = &f;
+    auto x = s.partition(&a,3);
+    while (x != NULL) {
+        cout << x->val << endl;
+        x = x->next;
+    }
+    return 0;
+}