← Back to Index

📚 Largest Odd Number in String – Java Cheat Sheet

📌 What Is It?

The Largest Odd Number in String problem involves finding the largest odd number that can be formed as a substring of the given numeric string. An odd number ends with an odd digit (1, 3, 5, 7, 9).

🧱 Pattern Template

Greedy Approach

class Solution {
    public String largestOddNumber(String num) {
        // Traverse the string from right to left
        for (int i = num.length() - 1; i >= 0; i--) {
            if ((num.charAt(i) - '0') % 2 != 0) {
                // Return the substring from 0 to i (inclusive)
                return num.substring(0, i + 1);
            }
        }
        return ""; // No odd number found
    }
}

▶️ View Animation

📊 Time Complexity

• Time Complexity: O(N), where N is the length of the string.
• Space Complexity: O(1), as no additional space is used.

✅ Use Cases

• Finding specific patterns in numeric strings.
• Optimizing substring operations in strings.

📘 Common LeetCode Problems

• 1903. Largest Odd Number in String [Easy] Greedy

🧪 Example

Input: num = "35427"
Output: "35427"

Explanation:
- The entire string is odd because it ends with 7, which is odd.

Input: num = "4206"
Output: ""

Explanation:
- No odd number can be formed because the string ends with an even digit.

💡 Pro Tips

• Traverse the string from right to left to find the first odd digit efficiently.
• If no odd digit is found, return an empty string.
• Use substring operations to extract the largest odd number.