"LeetCode Zero Basic Guide" (Ninth Lecture) Simple Recursion

172. Zero after factorial

class Solution {
    
    
public:
    int trailingZeroes(int n) {
    
    
        if(n==0) return 0;
        int sum=0,m=n;
        while(m%5==0) m/=5,sum++;
        return sum+trailingZeroes(n-1); 
    }
};
class Solution {
    
    
public:
    int trailingZeroes(int n) {
    
    
        int ans=0;
        for(int i=1;i<=n;i++) {
    
    
            int j=i;
            while(j%5==0) {
    
    
                ans++;
                j/=5;
            }
        }
        return ans;
    }
};

1342. Number of operations to change numbers to 0

class Solution {
    
    
public:
    int numberOfSteps(int num) {
    
    
        if(num==0) return 0;
        if(num%2) return 1+numberOfSteps(num-1);
        return 1+numberOfSteps(num/2);
    }
};

222. The number of nodes in a complete binary tree

/**
 * 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 countNodes(TreeNode* root) {
    
    
        if(root==nullptr) return 0;
        return countNodes(root->left)+countNodes(root->right)+1;
    }
};

LCP 44. Opening Ceremony Fireworks

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
    
    
public:
    unordered_map<int,int>mp;
    void dfs(TreeNode *root) {
    
    
        if(root==NULL) return;
        mp[root->val]++;
        dfs(root->left),dfs(root->right);
    }
    int numColor(TreeNode* root) {
    
    
        mp.clear();
        dfs(root);
        return mp.size();
    }
};

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