Number of Steps to Reduce a Number to Zero LeetCode Solution - The Coding Shala

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 In this post, we will learn how to solve LeetCode's Number of Steps to Reduce a Number to Zero problem and will implement its solution in Java.

Number of Steps to Reduce a Number to Zero Problem

Given a non-negative integer num, return the number of steps to reduce it to zero. If the current number is even, you have to divide it by 2, otherwise, you have to subtract 1 from it.

Example 1:
Input: num = 14
Output: 6
Explanation: 
Step 1) 14 is even; divide by 2 and obtain 7. 
Step 2) 7 is odd; subtract 1 and obtain 6.
Step 3) 6 is even; divide by 2 and obtain 3. 
Step 4) 3 is odd; subtract 1 and obtain 2. 
Step 5) 2 is even; divide by 2 and obtain 1. 
Step 6) 1 is odd; subtract 1 and obtain 0.

Practice this problem on LeetCode.

LeetCode - Number of Steps to Reduce a Number to Zero Java Solution

Approach 1

A simple iterative approach using the loop.

Java Program: 

class Solution {
    public int numberOfSteps (int num) {
        int ans = 0;
        while(num != 0) {
            if(num%2 == 0) {
                num /= 2;
            } else num--;
            ans++;
        }
        return ans;
    }
}

Approach 2

Using Bit Manipulation.

Java Program: 

class Solution {
    public int numberOfSteps (int num) {
        if(num == 0) return 0;
        int ans = 0;
        while(num != 0) {
            if((num & 1) == 1) ans = ans+2;
            else ans++;
            num = num >> 1;
        }
        //-1 for last 1 bit, we only subtract it not divide it
        //so only +1 is required in ans
        return ans-1;
    }
}


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