剑指offer专项突击版第15天

剑指 Offer II 044. 二叉树每层的最大值

简单的层序遍历

class Solution {
    
public:
    vector<int> largestValues(TreeNode* root) {
    
        if(!root) return {
    };
        queue<TreeNode*> que;
        que.push(root);
        vector<int> res;
        while(que.size()) {
    
            int sz = que.size();
            int maxx = INT_MIN;
            for(int i = 0; i < sz; i++) {
    
                auto cur = que.front(); que.pop();
                maxx = max(maxx,cur->val);
                if(cur->left) que.push(cur->left);
                if(cur->right) que.push(cur->right);
            }
            res.push_back(maxx);
        }
        return res;
    }
};

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剑指 Offer II 045. 二叉树最底层最左边的值

层序遍历，每次记录一层序列如果有下一层则清除当前序列并开始记录下一层序列，最终返回第一个就是最底层最左边的结点了

class Solution {
    
public:
    int findBottomLeftValue(TreeNode* root) {
    
        queue<TreeNode*> que;
        que.push(root);
        vector<int> backup;
        while(que.size()){
    
            int sz = que.size();
            backup.clear();
            for(int i = 0; i < sz; i++) {
    
                auto cur = que.front(); que.pop();
                backup.push_back(cur->val);
                if(cur->left) que.push(cur->left);
                if(cur->right) que.push(cur->right);
            }
        }
        return backup[0];
    }
};

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剑指 Offer II 046. 二叉树的右侧视图
层序遍历记录每一层最后一个即可

class Solution {
    
public:
    vector<int> rightSideView(TreeNode* root) {
    
        if(!root) return {
    };
        que<TreeNode*> que;
        que.push(root);
        vector<int> res;
        while(que.size()) {
    
            int last = -1, sz = que.size();
            for(int i = 0; i < sz; i++) {
    
                auto cur = que.front(); que.pop();
                last = cur->val;
                if(cur->left) que.push(cur->left);
                if(cur->right) que.push(cur->right);
            }
            res.push_back(last);
        }
        return res;
    }
};