feat(564): Hard

Given a string n representing an integer, return the closest integer (not including itself), which is a palindrome. If there is a tie, return the smaller one.

The closest is defined as the absolute difference minimized between two integers.

Example 1:

Input: n = "123"
Output: "121"
Example 2:

Input: n = "1"
Output: "0"
Explanation: 0 and 2 are the closest palindromes but we return the smallest which is 0.

Constraints:

1 <= n.length <= 18
n consists of only digits.
n does not have leading zeros.
n is representing an integer in the range [1, 1018 - 1].

internal/Leetcode/564/564.go

@@ -0,0 +1,39 @@
+package _564
+
+import (
+	"math"
+	"strconv"
+)
+
+func nearestPalindromic(n string) string {
+	l := len(n)
+	res := []int{int(math.Pow10(l-1)) - 1, int(math.Pow10(l)) + 1}
+	left, _ := strconv.Atoi(n[:(l+1)/2])
+	for _, x := range []int{left - 1, left, left + 1} {
+		y := x
+		if l&1 == 1 {
+			y /= 10
+		}
+		for ; y > 0; y /= 10 {
+			x = x*10 + y%10
+		}
+		res = append(res, x)
+	}
+	ans := -1
+	x, _ := strconv.Atoi(n)
+	for _, t := range res {
+		if t != x {
+			if ans == -1 || abs(t-x) < abs(ans-x) || abs(t-x) == abs(ans-x) && t < ans {
+				ans = t
+			}
+		}
+	}
+	return strconv.Itoa(ans)
+}
+
+func abs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}

internal/Leetcode/564/564_test.go

@@ -0,0 +1,34 @@
+package _564
+
+import (
+	"testing"
+)
+
+func Test_nearestPalindromic(t *testing.T) {
+	type args struct {
+		n string
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{
+			name: "Example 1",
+			args: args{n: "123"},
+			want: "121",
+		},
+		{
+			name: "Example 2",
+			args: args{n: "1"},
+			want: "0",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := nearestPalindromic(tt.args.n); got != tt.want {
+				t.Errorf("nearestPalindromic() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}