Check if Number Has Equal Digit Count and Digit Value

Problem Description

You are given a 0-indexed string num of length n consisting of digits. Return true if for every index i in the range 0 <= i < n, the digit i occurs num[i] times in num, otherwise return false.

Key Insights

• Each character in the string represents a digit, and its value indicates how many times the index digit should appear in the string.
• The maximum length of the input string is 10, which means we can efficiently count occurrences without performance concerns.
• A hash table (or array) can be used to count occurrences of each digit from 0 to 9.

Space and Time Complexity

Time Complexity: O(n)
Space Complexity: O(1) (Fixed size array for counting digits)

Solution

To solve the problem, we will use an array to count the occurrences of each digit from 0 to 9 based on the values of the digits in the input string. We will iterate through the string to populate the counts and then verify that each index matches the expected count according to the digit values.

The steps are as follows:

1. Initialize a count array of size 10 (for digits 0-9).
2. Loop through the string to count the occurrences of each digit.
3. Loop through the count array and check if the count matches the corresponding digit value in the string.
4. Return true if all conditions are satisfied, otherwise return false.

Code Solutions