268 篇文章 含有標籤「leetcode」

class Solution {
public:
    int hIndex(vector<int>& citations)
    {
        // Sort the citations in descending order

        // Initialize the index variable

        // Loop through the sorted citations array
        // Check if the citation count is greater than the current index
            // Increment the index
        // Return the H-Index
    }
};

class Solution {
public:
    int hIndex(vector<int>& citations)
    {
        sort(citations.rbegin(), citations.rend());
        int i = 0;
        while (i < citations.size() && citations[i] > i) ++i;
        return i;
    }
};

class Solution {
public:
    // Function to calculate the H-Index given a list of citation counts
    int hIndex(vector<int>& citations)
    {
        // Map to store the frequency of each citation count

        // Populate the map with citation counts and their frequencies

        // Convert the map to a vector of pairs and sort it in descending order of citation counts
        // m.rbegin() and m.rend() reverse the order of the map

        // Initialize the count of papers that have at least 'cnt' citations

        // Iterate through the sorted list of citation counts and their frequencies
        for ()
        {
            // If the current citation count is greater than the current count plus the number of papers with this citation count
            if ()
            {
                // Increase the count by the number of papers with this citation count
            }
            // If the current citation count is equal to the current count plus the number of papers with this citation count
            else if ()
            {
                // Return the current citation count as the H-Index
            }
            // If the current citation count is less than the current count plus the number of papers with this citation count
            else
            {
                // Return the maximum of the current citation count and the current count as the H-Index
            }
        }
        // If we have iterated through all the citation counts and not returned, return the count as the H-Index
    }
};

class Solution {
public:
    int hIndex(vector<int>& citations)
    {
        map<int, int> m;
        for (int i = 0; i < citations.size(); ++i) ++m[citations[i]];

        vector<pair<int, int>> q(m.rbegin(), m.rend());

        int cnt = 0;
        for (int i = 0; i < q.size(); ++i)
        {
            if (q[i].first > cnt + q[i].second)
            {
                cnt += q[i].second;
            }
            else if (q[i].first == cnt + q[i].second)
            {
                return q[i].first;
            }
            else
            {
                return max(q[i].first, cnt);
            }
        }
        return cnt;
    }
};

/*
 * @lc app=leetcode id=273 lang=cpp
 *
 * [273] Integer to English Words
 *
 * https://leetcode.com/problems/integer-to-english-words/description/
 *
 * algorithms
 * Hard (34.09%)
 * Likes:    3738
 * Dislikes: 6794
 * Total Accepted:    544.8K
 * Total Submissions: 1.6M
 * Testcase Example:  '123'
 *
 * Convert a non-negative integer num to its English words representation.
 *
 *
 * Example 1:
 *
 *
 * Input: num = 123
 * Output: "One Hundred Twenty Three"
 *
 *
 * Example 2:
 *
 *
 * Input: num = 12345
 * Output: "Twelve Thousand Three Hundred Forty Five"
 *
 *
 * Example 3:
 *
 *
 * Input: num = 1234567
 * Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty
 * Seven"
 *
 *
 *
 * Constraints:
 *
 *
 * 0 <= num <= 2^31 - 1
 *
 *
 */

// @lc code=start
class Solution {
public:
    string numberToWords(int num) {
       if (num == 0) return "Zero";

        vector<pair<int, string>> units = {
            {1000000000, "Billion"},
            {1000000, "Million"},
            {1000, "Thousand"},
            {1, ""}
        };

        string res;
        for (auto& [val, name] : units) {
            if (num >= val) {
                string segment = helper(num / val);
                res += segment + (name.empty() ? "" : " " + name) + " ";
                num %= val;
            }
        }
        while (!res.empty() && res.back() == ' ') res.pop_back();
        return res;
    }
    string helper(int num) {
        vector<string> below_20 = {
            "", "One", "Two", "Three", "Four", "Five", "Six", "Seven",
            "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen",
            "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"
        };
        vector<string> tens = {
            "", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"
        };
        string res;
        if (num < 20) {
            res = below_20[num];
        } else if (num < 100) {
            res = tens[num / 10];
            if (num % 10 != 0) {
                res += " " + helper(num % 10);
            }
            return res;
        } else {
            res = below_20[num / 100] + " Hundred";
            if (num % 100 != 0) {
                res += " " + helper(num % 100);
            }
        }
        return res;
    }
};
// @lc code=end

class Codec {
public:

    // Encodes a list of strings to a single string.
    string encode(vector<string>& strs) {
        string res = "";
        for (auto& a : strs) {
            // 轉成size/字串size/字串size/字串
            // ["Hello","World"] -> 5/Hello5/World
            res.append(to_string(a.size())).append("/").append(a);
        }
        return res;
    }

    // Decodes a single string to a list of strings.
    vector<string> decode(string s) {
        vector<string> res;
        int i = 0;
        while (i < s.size()) {
            // 找到分隔號的位置
            auto found = s.find("/", i);

            // 得到字串長度
            int len = stoi(s.substr(i, found - i));

            // 將字串推到 array
            res.push_back(s.substr(found + 1, len));

            // 下一根指針
            i = found + len + 1;
        }
        return res;
    }
};

// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.decode(codec.encode(strs));

class Solution {
public:
    int missingNumber(vector<int>& nums)
    {
        int n = nums.size();
        for(int i = 0; i < nums.size(); i++)
        {
            n += i - nums[i];
        }
        return n;
    }
};

class Solution {
public:
    bool validTree(int n, vector<vector<int>>& edges)
    {
        vector<vector<int>> graph(n, vector<int>());
        for (auto& edge : edges)
        {
            graph[edge[0]].push_back(edge[1]);
            graph[edge[1]].push_back(edge[0]);
        }

        unordered_set<int> seen;
        return dfs(graph, seen, 0, -1) && seen.size() == n;
    }

    bool dfs(vector<vector<int>>& graph, unordered_set<int>& seen, int node, int parent)
    {
        if (seen.count(node)) return false;

        seen.insert(node);

        for(int nei : graph[node])
        {
            if (parent != nei)
            {
                if (!dfs(graph, seen, nei, node))
                    return false;
            }
        }
        return true;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> res;
        dfs(root, "", res);
        return res;
    }

    void dfs(TreeNode* root, string out, vector<string>& res) {
        if(!root->left && !root->right) {
            res.push_back(out + to_string(root->val));
        }
        if(root->left) {
            dfs(root->left, out + to_string(root->val) + "->", res);
        }
        if(root->right) {
            dfs(root->right, out + to_string(root->val) + "->", res);
        }
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> res;
        // base case
        if(!root) return res;

        // 如果沒有左右子節點，則返回 root
        if(!root->left && !root->right) {
            return {to_string(root->val)};
        }

        // 找左側
        for(auto s : binaryTreePaths(root->left)) {
            res.push_back(to_string(root->val) + "->" + s);
        }

        // 找右側
        for(auto s : binaryTreePaths(root->right)) {
            res.push_back(to_string(root->val) + "->" + s);
        }

        return res;
    }
};

class Solution {
public:
    int minMeetingRooms(vector<vector<int>>& intervals) {
        int n = intervals.size();

        sort(intervals.begin(), intervals.end());
        priority_queue<int, vector<int>, greater<int>> minHeap;

        // #0: minHeap = [30];
        // #1: minHeap = [10, 30];
        // #2: minHeap = [10, 20];
        for (auto& interval : intervals) {
            if (!minHeap.empty() && interval[0] >= minHeap.top()) {
                minHeap.pop();
            }
            minHeap.push(interval[1]);
        }
        return minHeap.size();
    }
};

class Solution {
public:
    bool canAttendMeetings(vector<vector<int>>& intervals) {
        int n = intervals.size();
        if (n == 0) return true;
        sort(intervals.begin(), intervals.end());
        for(int i = 0; i < n - 1; i++) {
            // 如果目前區間的 endtime 比下一個區間的 start time 大的話
            // 代表有 overlap
            if (intervals[i].back() > intervals[i + 1].front())
                return false;
        }
        return true;
    }
};

class Solution {
public:
    bool isAnagram(string s, string t)
    {
        if (s.size() != t.size()) return false;

        unordered_map<char, int> m;

        for(auto& c : s) ++m[c];

        for (auto& c : t)
        {
            if (m.count(c))
            {
                --m[c];
                if (!m[c]) m.erase(c);
            }
        }
        return !m.size();
    }
};