# 1903. Largest Odd Number in String

## Intuition

To find the **largest-valued odd integer substring**, we don't need to check every possible substring.\
Since the original string represents a number and all digits are ordered from most significant to least significant (like a real number), the largest odd-valued substring will simply be the **longest prefix** (from the start) ending at the **rightmost odd digit**.

If we find the **last odd digit** in the string while iterating from the end, the substring from the start to that index will be our answer.

## Complexity

| Space Complexity | Time Complexity |
| ---------------- | --------------- |
| $$\text{O}(1)$$  | $$\text{O}(n)$$ |

## Code

```java
public String largestOddNumber(String numberStr) {
    // Traverse from end to start
    for (int index = numberStr.length() - 1; index >= 0; --index) {
        // Convert character to integer and check if it's odd
        if ((numberStr.charAt(index) - '0') % 2 != 0) {
            // Return the substring from start to current index (inclusive)
            return numberStr.substring(0, index + 1);
        }
    }

    // No odd digit found, return empty string
    return "";
}
```


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