Add solution and test-cases for problem 3039

leetcode/3001-3100/3039.Apply-Operations-to-Make-String-Empty/README.md

@@ -1,28 +1,37 @@
 # [3039.Apply Operations to Make String Empty][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+You are given a string `s`.
+
+Consider performing the following operation until `s` becomes **empty**:
+
+- For **every** alphabet character from `'a'` to `'z'`, remove the **first** occurrence of that character in `s` (if it exists).
+
+For example, let initially `s = "aabcbbca"`. We do the following operations:
+
+- Remove the underlined characters `s = "aabcbbca"`. The resulting string is `s = "abbca"`.
+- Remove the underlined characters `s = "abbca"`. The resulting string is `s = "ba"`.
+- Remove the underlined characters `s = "ba"`. The resulting string is `s = ""`.
+
+Return the value of the string `s` right **before** applying the **last** operation. In the example above, answer is `"ba"`.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: s = "aabcbbca"
+Output: "ba"
+Explanation: Explained in the statement.
 ```
 
-## 题意
-> ...
-
-## 题解
+**Example 2:**
 
-### 思路1
-> ...
-Apply Operations to Make String Empty
-```go
 ```
-
+Input: s = "abcd"
+Output: "abcd"
+Explanation: We do the following operation:
+- Remove the underlined characters s = "abcd". The resulting string is s = "".
+The string just before the last operation is "abcd".
+```
 
 ## 结语
 

leetcode/3001-3100/3039.Apply-Operations-to-Make-String-Empty/Solution.go

@@ -1,5 +1,28 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+import (
+	"sort"
+	"strings"
+)
+
+func Solution(s string) string {
+	count := [26][2]int{}
+	mc := 0
+	for i, b := range s {
+		count[b-'a'][0]++
+		count[b-'a'][1] = i
+		mc = max(mc, count[b-'a'][0])
+	}
+	indies := []int{}
+	for i := 0; i < 26; i++ {
+		if count[i][0] == mc {
+			indies = append(indies, count[i][1])
+		}
+	}
+	sort.Ints(indies)
+	sb := strings.Builder{}
+	for _, i := range indies {
+		sb.WriteByte(s[i])
+	}
+	return sb.String()
 }

leetcode/3001-3100/3039.Apply-Operations-to-Make-String-Empty/Solution_test.go

@@ -10,12 +10,11 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		inputs string
+		expect string
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", "aabcbbca", "ba"},
+		{"TestCase2", "abcd", "abcd"},
 	}
 
 	//	开始测试
@@ -30,10 +29,10 @@ func TestSolution(t *testing.T) {
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }