Remove Duplicates from Sorted List II

本文详细解析了一种用于链表数据结构的去重算法,通过遍历链表并使用额外指针来移除重复元素,确保链表中每个元素都是唯一的。文章通过具体实例展示了算法的工作原理,并提供了完整的C++代码实现。

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解题思路,举几个例子

1->1 

1->1->2->2

1->2->2->3

1->2->2

思路也就清晰了:

循环遍历每个元素:

1、从头就开始重复的,head直接置为下一个跟头重复元素不同的结点,继续(当然可能还继续重复)

2、不从头重复的,考虑是去掉重复的所有元素,所以要多一个指针,指向重复的第一个结点的前一个

容易出错的地方:

1、判断循环的指针p是否为空  一定要先判断  eg:

  while(p&& head->val==p->val)
在1->1的例子中,若p第二次循环时候已经为空,访问p的val当然会出错!

2、判断结束

1->2->2  也是类似,要先判断p是否已经结束,否则访问p的next也是错!

3、细节

 eg:t最初是指向head的,所以head.val==t.val是必须的!


class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        //重复的直接删除
        ListNode *t=head;
        if(t==NULL) return t;
        if(t->next==NULL) return head;
        //头可能重复
        ListNode *pre=t;
        ListNode *p=t->next;
         while(p)
         {
             
                while(p&& head->val==p->val) //从头重复 但是,若p为空,再访问p的val就是有问题的!!!
                //while(head->val==p->val && p)  //所以注释掉这段
                 {
                     t=p;
                     p=p->next;
                 
                 }
                
                 if(t->val==head->val && t!=head)//如果从头重复,直接head重新赋值
                 {
                  head=p;
                }
              
                 
                
                if(p &&head->val!=p->val)//如果没有从头重复
                {
                   
                    while(p && t->val==p->val )//如果重复
                    {
                        p=p->next;
                    }
                    if(t->next==p)//如果没有重复
                    {
                        pre=t;
                        t=t->next;
                        p=p->next;
                    }
                    else//重复处理:
                    {
                        pre->next=p;
                        t=p;
                        if(p==NULL) break;//如果已经到最后  直接结束循环,否则再访问next肯定出错!
                        else     p=p->next;
                    }
                     
                }
      
              
             
         }
         
         return head;
        
    }
};


1. Two Sum 2. Add Two Numbers 3. Longest Substring Without Repeating Characters 4. Median of Two Sorted Arrays 5. Longest Palindromic Substring 6. ZigZag Conversion 7. Reverse Integer 8. String to Integer (atoi) 9. Palindrome Number 10. Regular Expression Matching 11. Container With Most Water 12. Integer to Roman 13. Roman to Integer 14. Longest Common Prefix 15. 3Sum 16. 3Sum Closest 17. Letter Combinations of a Phone Number 18. 4Sum 19. Remove Nth Node From End of List 20. Valid Parentheses 21. Merge Two Sorted Lists 22. Generate Parentheses 23. Swap Nodes in Pairs 24. Reverse Nodes in k-Group 25. Remove Duplicates from Sorted Array 26. Remove Element 27. Implement strStr() 28. Divide Two Integers 29. Substring with Concatenation of All Words 30. Next Permutation 31. Longest Valid Parentheses 32. Search in Rotated Sorted Array 33. Search for a Range 34. Find First and Last Position of Element in Sorted Array 35. Valid Sudoku 36. Sudoku Solver 37. Count and Say 38. Combination Sum 39. Combination Sum II 40. First Missing Positive 41. Trapping Rain Water 42. Jump Game 43. Merge Intervals 44. Insert Interval 45. Unique Paths 46. Minimum Path Sum 47. Climbing Stairs 48. Permutations 49. Permutations II 50. Rotate Image 51. Group Anagrams 52. Pow(x, n) 53. Maximum Subarray 54. Spiral Matrix 55. Jump Game II 56. Merge k Sorted Lists 57. Insertion Sort List 58. Sort List 59. Largest Rectangle in Histogram 60. Valid Number 61. Word Search 62. Minimum Window Substring 63. Unique Binary Search Trees 64. Unique Binary Search Trees II 65. Interleaving String 66. Maximum Product Subarray 67. Binary Tree Inorder Traversal 68. Binary Tree Preorder Traversal 69. Binary Tree Postorder Traversal 70. Flatten Binary Tree to Linked List 71. Construct Binary Tree from Preorder and Inorder Traversal 72. Construct Binary Tree from Inorder and Postorder Traversal 73. Binary Tree Level Order Traversal 74. Binary Tree Zigzag Level Order Traversal 75. Convert Sorted Array to Binary Search Tree 76. Convert Sorted List to Binary Search Tree 77. Recover Binary Search Tree 78. Sum Root to Leaf Numbers 79. Path Sum 80. Path Sum II 81. Binary Tree Maximum Path Sum 82. Populating Next Right Pointers in Each Node 83. Populating Next Right Pointers in Each Node II 84. Reverse Linked List 85. Reverse Linked List II 86. Partition List 87. Rotate List 88. Remove Duplicates from Sorted List 89. Remove Duplicates from Sorted List II 90. Intersection of Two Linked Lists 91. Linked List Cycle 92. Linked List Cycle II 93. Reorder List 94. Binary Tree Upside Down 95. Binary Tree Right Side View 96. Palindrome Linked List 97. Convert Binary Search Tree to Sorted Doubly Linked List 98. Lowest Common Ancestor of a Binary Tree 99. Lowest Common Ancestor of a Binary Search Tree 100. Binary Tree Level Order Traversal II
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