剑指Offer刷题日常

剑指 Offer 03. 数组中重复的数字

• p40

class Solution {
public:
    int findRepeatNumber(vector<int>& nums) {
        int length = nums.size();
        if (length <= 0)
        {
            return false;
        }
        for (int i = 0; i < length; ++i)
        {
            if (nums[i] < 0 || nums[i] > length - 1)
            {
                return false;
            }
        }
        for (int i = 0; i < length; ++i)
        {
            while (nums[i] != i)
            {
                if (nums[i] == nums[nums[i]])
                {
                    return nums[i];
                }
                int t = nums[i];
                nums[i] = nums[t];
                nums[t] = t;
            }
        }
        return false;
    }
};

剑指 Offer 04. 二维数组中的查找

class Solution:
    def findNumberIn2DArray(self, matrix: List[List[int]], target: int) -> bool:
        if matrix == [] or matrix == [[]]:
            return False
        row = len(matrix)
        col = len(matrix[0])
        if target < matrix[0][0] or target > matrix[row-1][col-1]:
            return False
        
        r, c = 0, col-1
        while r < row and c >= 0:
            if matrix[r][c] == target:
                return True
            if matrix[r][c] < target:
                r = r + 1
            else:
                c = c - 1
        return False

剑指 Offer 05. 替换空格

class Solution {
public:
    string replaceSpace(string s) {
        int cnt = 0, len = s.size();
        // 统计空格数量
        for (char c : s) 
        {
            if (c == ' ')
                cnt++;
        }
        // 修改 s 长度
        s.resize(len + 2 * cnt);
        // 倒序遍历修改
        for (int i = len - 1, j = s.size()-1; i < j; --i, --j)
        {
            if (s[i] != ' ')
            {
                s[j] = s[i];
            }
            else
            {
                s[j - 2] = '%';
                s[j - 1] = '2';
                s[j] = '0';
                j -= 2;
            }
        }
        return s;
    }
};

剑指 Offer 06. 从尾到头打印链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> reversePrint(ListNode* head) {
        stack<ListNode*> nodes;
        vector<int> ans;

        ListNode *pNode = head;
        while (pNode != nullptr)
        {
            nodes.push(pNode);
            pNode = pNode->next;
        }
        while (!nodes.empty())
        {
            pNode = nodes.top();
            ans.push_back(pNode->val);
            nodes.pop();
        }
        return ans;
    }
};

or

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> reversePrint(ListNode* head) {
        vector<int> ans;
        reverseRec(head, ans);
        return ans;
    }
    
    void reverseRec(ListNode* head, vector<int>& ans)
    {
        if (head != nullptr)
        {
            if (head->next != nullptr)
            {
                reverseRec(head->next, ans);
            }
            ans.push_back(head->val);
        }
    }
};