3798-LargestEvenNumber.go

package main 

// 3798. Largest Even Number
// You are given a string s consisting only of the characters '1' and '2'.

// You may delete any number of characters from s without changing the order of the remaining characters.

// Return the largest possible resultant string that represents an even integer. 
// If there is no such string, return the empty string "".

// Example 1:
// Input: s = "1112"
// Output: "1112"
// Explanation:
// The string already represents the largest possible even number, so no deletions are needed.

// Example 2:
// Input: s = "221"
// Output: "22"
// Explanation:
// Deleting '1' results in the largest possible even number which is equal to 22.

// Example 3:
// Input: s = "1"
// Output: ""
// Explanation:
// There is no way to get an even number.

// Constraints:
//     1 <= s.length <= 100
//     s consists only of the characters '1' and '2'.

import "fmt"

// time: O(n), space: O(1)
func largestEven(s string) string {
    i := len(s) - 1
    for i >= 0 && s[i] == '1' {
        i--
    }
    return s[:i + 1]
}

func main() {
    // Example 1:
    // Input: s = "1112"
    // Output: "1112"
    // Explanation:
    // The string already represents the largest possible even number, so no deletions are needed.
    fmt.Println(largestEven("1112")) // "1112"
    // Example 2:
    // Input: s = "221"
    // Output: "22"
    // Explanation:
    // Deleting '1' results in the largest possible even number which is equal to 22.
    fmt.Println(largestEven("221")) // "22"
    // Example 3:
    // Input: s = "1"
    // Output: ""
    // Explanation:
    // There is no way to get an even number.
    fmt.Println(largestEven("1")) // ""

    fmt.Println(largestEven("1111111111")) // ""
    fmt.Println(largestEven("2222222222")) // "2222222222"
    fmt.Println(largestEven("2222211111")) // "22222"
    fmt.Println(largestEven("1111122222")) // "1111122222"
    fmt.Println(largestEven("1212121212")) // "1212121212"
    fmt.Println(largestEven("2121212121")) // "2121212121"
}