Binary Number to Decimal Number

Problem

Given a Binary Number B, find its decimal equivalent.

Examples:

Example 1:

Input: B = 10001000
Output: 136

Example 2:

Input: B = 101100
Output: 44

Your task:

You don't need to read or print anything. Your task is to complete the function binary_to_decimal() which takes the binary number as string input parameter and returns its decimal equivalent.

• Expected Time Complexity: $O(K * Log(K))$, where K is number of bits in binary number.
• Expected Auxiliary Space: $O(1)$

Constraints:

• $1 <=$ number of bits in binary number $<= 16$

Solution

Python

def binary_to_decimal(self, str):
	num = int(str);
    dec_value = 0;
    base = 1;
    temp = num;
    while(temp):
        last_digit = temp % 10;
        temp = int(temp / 10);
        dec_value += last_digit * base;
        base = base * 2;
    return dec_value;

Java

public int binary_to_decimal(String str) {
    int decValue = 0;
    int base = 1;  
    for (int i = str.length() - 1; i >= 0; i--) {
        if (str.charAt(i) == '1') {
            decValue += base;
        }
        base = base * 2;  
    }
    return decValue;
}

C++

int binary_to_decimal(string str) {
    unsigned long long num = bitset<64>(str).to_ullong();
    int decValue = static_cast<int>(num);
    return decValue;
}

C

int binary_to_decimal(char str[]) {
    int len = strlen(str);
    int dec_value = 0;
    int base = 1; 
    int i;
    for (i = len - 1; i >= 0; i--) {
        if (str[i] == '1') {
            dec_value += base;
        }
        base *= 2;
    }
    return dec_value;
}

• Time Complexity: $O(K * Log(K))$
• Auxiliary Space: $O(1)$