3884-FirstMatchingCharacterFromBothEnds.go

package main

// 3884. First Matching Character From Both Ends
// You are given a string s of length n consisting of lowercase English letters.

// Return the smallest index i such that s[i] == s[n - i - 1].

// If no such index exists, return -1.

// Example 1:
// Input: s = "abcacbd"
// Output: 1
// Explanation:
// At index i = 1, s[1] and s[5] are both 'b'.
// No smaller index satisfies the condition, so the answer is 1.

// Example 2:
// Input: s = "abc"
// Output: 1
// Explanation:
// ​​​​​​​At index i = 1, the two compared positions coincide, so both characters are 'b'.
// No smaller index satisfies the condition, so the answer is 1.

// Example 3:
// Input: s = "abcdab"
// Output: -1
// Explanation:
// ​​​​​​​For every index i, the characters at positions i and n - i - 1 are different.
// Therefore, no valid index exists, so the answer is -1.

// Constraints:
//     1 <= n == s.length <= 100
//     s consists of lowercase English letters.

import "fmt"

func firstMatchingIndex(s string) int {
    low, high := 0, len(s) - 1
    for low <= high {
        if s[low] == s[high] {
            return low
        }
        low++
        high--
    }
    return -1
}

func main() {
    // Example 1:
    // Input: s = "abcacbd"
    // Output: 1
    // Explanation:
    // At index i = 1, s[1] and s[5] are both 'b'.
    // No smaller index satisfies the condition, so the answer is 1.
    fmt.Println(firstMatchingIndex("abcacbd")) // 1
    // Example 2:
    // Input: s = "abc"
    // Output: 1
    // Explanation:
    // ​​​​​​​At index i = 1, the two compared positions coincide, so both characters are 'b'.
    // No smaller index satisfies the condition, so the answer is 1.
    fmt.Println(firstMatchingIndex("abc")) // 1
    // Example 3:
    // Input: s = "abcdab"
    // Output: -1
    // Explanation:
    // ​​​​​​​For every index i, the characters at positions i and n - i - 1 are different.
    // Therefore, no valid index exists, so the answer is -1.
    fmt.Println(firstMatchingIndex("abcdab")) // -1

    fmt.Println(firstMatchingIndex("bluefrog")) // -1
    fmt.Println(firstMatchingIndex("leetcode")) // -1
    fmt.Println(firstMatchingIndex("freewu")) // 2
}