Add solution and test-cases for problem 2843

leetcode/2801-2900/2843.Count-Symmetric-Integers/README.md

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+# [2843.Count Symmetric Integers][title]
+
+## Description
+You are given two positive integers `low` and `high`.
+
+An integer `x` consisting of `2 * n` digits is **symmetric** if the sum of the first `n` digits of `x` is equal to the sum of the last `n` digits of `x`. Numbers with an odd number of digits are never symmetric.
+
+Return the **number of symmetric** integers in the range `[low, high]`.
+
+**Example 1:**
+
+```
+Input: low = 1, high = 100
+Output: 9
+Explanation: There are 9 symmetric integers between 1 and 100: 11, 22, 33, 44, 55, 66, 77, 88, and 99.
+```
+
+**Example 2:**
+
+```
+Input: low = 1200, high = 1230
+Output: 4
+Explanation: There are 4 symmetric integers between 1200 and 1230: 1203, 1212, 1221, and 1230.
+```
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我 GitHub 上的 LeetCode 题解：[awesome-golang-algorithm][me]
+
+[title]: https://leetcode.com/problems/count-symmetric-integers
+[me]: https://github.com/kylesliu/awesome-golang-algorithm

leetcode/2801-2900/2843.Count-Symmetric-Integers/Solution.go

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+package Solution
+
+import "fmt"
+
+func Solution(low int, high int) int {
+	var ok func(int) bool
+	ok = func(n int) bool {
+		s := fmt.Sprintf("%d", n)
+		l := len(s)
+		if l&1 == 1 {
+			return false
+		}
+		// 1 2, 3, 4
+		left, right := 0, 0
+		for start, end := 0, l-1; start < end; start, end = start+1, end-1 {
+			left += int(s[start] - '0')
+			right += int(s[end] - '0')
+		}
+		return left == right
+	}
+	cnt := 0
+	for i := low; i <= high; i++ {
+		if ok(i) {
+			cnt++
+		}
+	}
+	return cnt
+}

leetcode/2801-2900/2843.Count-Symmetric-Integers/Solution_test.go

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+package Solution
+
+import (
+	"reflect"
+	"strconv"
+	"testing"
+)
+
+func TestSolution(t *testing.T) {
+	//	测试用例
+	cases := []struct {
+		name      string
+		low, high int
+		expect    int
+	}{
+		{"TestCase1", 1, 100, 9},
+		{"TestCase2", 1200, 1230, 4},
+	}
+
+	//	开始测试
+	for i, c := range cases {
+		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
+			got := Solution(c.low, c.high)
+			if !reflect.DeepEqual(got, c.expect) {
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v",
+					c.expect, got, c.low, c.high)
+			}
+		})
+	}
+}
+
+// 压力测试
+func BenchmarkSolution(b *testing.B) {
+}
+
+// 使用案列
+func ExampleSolution() {
+}