1903-LargestOddNumberInString.go

package main

// 1903. Largest Odd Number in String
// You are given a string num, representing a large integer. 
// Return the largest-valued odd integer (as a string) that is a non-empty substring of num, 
// or an empty string "" if no odd integer exists.

// A substring is a contiguous sequence of characters within a string.

// Example 1:
// Input: num = "52"
// Output: "5"
// Explanation: The only non-empty substrings are "5", "2", and "52". "5" is the only odd number.

// Example 2:
// Input: num = "4206"
// Output: ""
// Explanation: There are no odd numbers in "4206".

// Example 3:
// Input: num = "35427"
// Output: "35427"
// Explanation: "35427" is already an odd number.

// Constraints:
//     1 <= num.length <= 10^5
//     num only consists of digits and does not contain any leading zeros.

import "fmt"

func largestOddNumber(num string) string {
    arr, i := []byte(num), len(num) - 1
    for ; i >= 0; i-- {
        if int(arr[i] - '0') % 2 == 1 { break } 
    }
    if i == -1 { return "" }
    return string(arr[:i + 1])
}

func main() {
    // Example 1:
    // Input: num = "52"
    // Output: "5"
    // Explanation: The only non-empty substrings are "5", "2", and "52". "5" is the only odd number.
    fmt.Println(largestOddNumber("52")) // "5"
    // Example 2:
    // Input: num = "4206"
    // Output: ""
    // Explanation: There are no odd numbers in "4206".
    fmt.Println(largestOddNumber("4206")) // ""
    // Example 3:
    // Input: num = "35427"
    // Output: "35427"
    // Explanation: "35427" is already an odd number.
    fmt.Println(largestOddNumber("35427")) // "35427"
}