LeetCode刷题系列(4)

class Solution {
public:
    static bool cmp(const pair<int, int>& x, const pair<int, int>& y) {
        return x.second > y.second;
    }
    vector<int> topKFrequent(vector<int>& nums, int k) {
        unordered_map<int, int> mp;
        vector<int> res;
        for(int x : nums) {
            mp[x]++;
        }
        vector<pair<int, int>> v(mp.begin(), mp.end());
        sort(v.begin(), v.end(), cmp);
        for(int i = 0; i < k; i++) {
            res.push_back(v[i].first);
        }
        return res;
    }
};

class MyCalendar {
private:
    map<int, int> events;
public:
    MyCalendar() {

    }
    
    bool book(int start, int end) {
        auto it = events.lower_bound(start);  //找到第一个>=start的区间
        // 与后一个时间段重叠
        if (it != events.end() && it->first < end) {
            return false;  //不能加入
        }
        // 与前一个时间段重叠
        if (it != events.begin() && (--it)->second > start) {
            return false;  //不能加入
        }
        events[start] = end;  //加入
        return true;
    }
};

class Solution {
public:
    bool containsNearbyAlmostDuplicate(vector<int>& nums, int k, int t) {
        int n = nums.size();
        for(int i = 0; i < n; i++) {
            for(int j = i + 1; j < n; j++) {
                if(abs((long long)nums[i] - nums[j]) <= t && abs(i - j) <= k) {
                    return true;
                }
            }
        }
        return false;
    }
};

class Solution {
public:
    bool containsNearbyAlmostDuplicate(vector<int>& nums, int k, int t) {
        int n = nums.size();
        set<int> rec;
        for (int i = 0; i < n; i++) {
            auto iter = rec.lower_bound(max(nums[i], INT_MIN + t) - t);
            if (iter != rec.end() && *iter <= min(nums[i], INT_MAX - t) + t) {
                return true;
            }
            rec.insert(nums[i]);
            if (i >= k) {
                rec.erase(nums[i - k]);  //滑动窗口
            }
        }
        return false;
    }
};

/**
 * 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<int> res;
    void dfs(TreeNode* root) {
        if(root) {
            dfs(root->left);
            res.push_back(root->val);
            dfs(root->right);
        }
    }
    bool findTarget(TreeNode* root, int k) {
        dfs(root);
        for(int x : res) {
            cout << x << " ";
        }
        int low = 0, high = res.size() - 1;
        while(low < high) {
            int mid = res[low] + res[high];
            if(mid == k) {
                return true;
            }else if(mid > k) {
                high--;
            }else {
                low++;
            }
        }
        return false;
    }
};

/**
 * 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:
    int sum = 0;
    TreeNode* convertBST(TreeNode* root) {
        if(root) {
            convertBST(root->right);
            // cout << root->val << " ";
            sum += root->val;
            root->val = sum;
            convertBST(root->left);
        }
        return root;
    }
};