代码随想录Day18

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LeetCode530. 二叉搜索树的最小绝对差

class Solution {
public:
    int getMinimumDifference(TreeNode* root) {
        vector<int> array;
        TreeNode* cur = root;
        stack<TreeNode*> s;
        int result = INT_MAX;
        while(cur || !s.empty()){
            while(cur){
                s.push(cur);
                cur = cur->left;
            }
            cur = s.top();
            s.pop();
            array.push_back(cur->val);
            cur = cur->right;
        }
        for(int i = 0; i < array.size() - 1; i++){
            result = min(array[i + 1] - array[i], result);
        }
        return result;
    }
};

LeetCode501.二叉搜索树的众数

class Solution {
public:
    vector<int> findMode(TreeNode* root) {
        TreeNode* cur = root;
        stack<TreeNode*> s;
        vector<int> array, result;
        int numTimes = 0, maxTimes = INT_MIN, nowNum;
        while(cur || !s.empty()){
            while(cur){
                s.push(cur);
                cur = cur->left;
            }
            cur = s.top();
            s.pop();
            array.push_back(cur->val);
            cur = cur->right;
        }
        nowNum = array[0];
        for(int i = 0; i < array.size(); i++){
            if(array[i] == nowNum){
                numTimes++;
            }
            if(array[i] != nowNum){
                if(numTimes == maxTimes){
                    result.push_back(nowNum);
                }else if(numTimes > maxTimes){
                    result.clear();
                    result.push_back(nowNum);
                    maxTimes = numTimes;
                }
                numTimes = 1;
                nowNum = array[i];
            }
            if(i == array.size() - 1){
                if(numTimes == maxTimes){
                    result.push_back(nowNum);
                }else if(numTimes > maxTimes){
                    result.clear();
                    result.push_back(nowNum);
                    maxTimes = numTimes;
                }
            }
        }
        return result;
    }
};

LeetCode236.二叉树最近公共祖先

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root == p || root == q || root == NULL)return root;

        TreeNode* left = lowestCommonAncestor(root->left, p, q);
        TreeNode* right = lowestCommonAncestor(root->right, p, q);

        if(left != NULL && right == NULL)return left;
        if(left == NULL && right != NULL)return right;
        if(left != NULL && right != NULL)return root;
        return NULL;
    }
};