Leetcode 54 59 61

本文介绍了解决螺旋矩阵遍历与生成问题的方法,并提供了一种高效的链表旋转算法实现。通过具体代码示例,展示了如何按照顺时针螺旋顺序遍历矩阵,以及如何生成螺旋排列的正方形矩阵。

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54.螺旋矩阵

题目描述:给定一个包含 m x n 个元素的矩阵(m 行, n 列),请按照顺时针螺旋顺序,返回矩阵中的所有元素。

思路:按照螺旋矩阵的顺序进行循环即可。(将循环终止条件设置为result.Count=m*n)。
代码:

public class Solution
{
    public IList<int> SpiralOrder(int[][] matrix)
    {
        int m = matrix.Length;
        int n = matrix[0].Length;
        List<int> result=new List<int>();
        result.AddRange(matrix[0]);
        int count = 0;
        while (result.Count<m*n)
        {
            for (int i = 1+count; i < m-count; i++)
            {
                if (result.Count < m * n)
                    result.Add(matrix[i][n - 1-count]);
            }
            for (int i = n - 2-count; i > -1+count; i--)
            {
                if (result.Count < m * n)
                    result.Add(matrix[m - 1-count][i]);
            }
            for (int i = m - 2-count; i > 0+count; i--)
            {
                if (result.Count < m * n)
                    result.Add(matrix[i][count]);
            }
            for (int i = 1+count; i < n - 1-count; i++)
            {
                if (result.Count < m * n)
                    result.Add(matrix[1+count][i]);
            }
            count++;
        }
        return result;
    }
}

59.螺旋矩阵II

题目描述:给定一个正整数 n,生成一个包含 1 到 n2 所有元素,且元素按顺时针顺序螺旋排列的正方形矩阵。

思路:和54题思路一致,对代码稍作修改。

public class Solution
{
    public int[][] GenerateMatrix(int n)
    {
        int[][] result=new int[n][];
        for (int i = 0; i < n; i++)
            result[i] = new int[n];
        for (int i = 0; i < n; i++)
            result[0][i] = i + 1;
        int temp=n+1;
        int count = 0;
        while (temp<n*n+1)
        {
            for (int i = 1 + count; i < n - count; i++)
            {
                if (temp < n * n + 1)
                {
                    result[i][n - 1 - count]=temp;
                    temp++;
                }
            }
            for (int i = n - 2 - count; i > -1 + count; i--)
            {
                if (temp < n * n + 1)
                {
                    result[n - 1 - count][i]=temp;
                    temp++;
                }
            }
            for (int i = n - 2 - count; i > 0 + count; i--)
            {
                if (temp < n * n + 1)
                {
                    result[i][count]=temp;
                    temp++;
                }
            }
            for (int i = 1 + count; i < n - 1 - count; i++)
            {
                if (temp < n * n + 1)
                {
                    result[1 + count][i]=temp;
                    temp++;
                }
            }
            count++;
        }
        return result;
    }
}

61.旋转链表

题目描述:给定一个链表,旋转链表,将链表每个节点向右移动 k 个位置,其中 k 是非负数。

思路:本题如果一个结点一个结点的移动会超出时间限制,只需对k做简单讨论,找到最终的头结点,将该结点及其之和的结点全部放到原头结点的前面即可。
代码如下:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution
{
    public ListNode RotateRight(ListNode head, int k)
    {
        if (head == null || k == 0 || head.next == null)
            return head;
        int len=1;
        ListNode b=head;
        while (b.next != null)
        {
            b = b.next;
            len++;
        }
        k = k % len;
        if(k==0)
           return head;
        ListNode i=head;
        ListNode j=head.next;
        for(int t=0;t<len-k-1;t++)
        {
                j = j.next;
                i = i.next;
        }
        b.next=head;
        head=j;
        i.next=null;
        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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