Merge pull request #841 from 0xff-dev/402

Add solution and test-cases for problem 402

Author: 6boris

leetcode/401-500/0402.Remove-K-Digits/README.md

@@ -1,28 +1,31 @@
 # [402.Remove K Digits][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
+Given string num representing a non-negative integer `num`, and an integer `k`, return the smallest possible integer after removing `k` digits from `num`.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: num = "1432219", k = 3
+Output: "1219"
+Explanation: Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.
 ```
 
-## 题意
-> ...
-
-## 题解
+**Example 2:**
 
-### 思路1
-> ...
-Remove K Digits
-```go
+```
+Input: num = "10200", k = 1
+Output: "200"
+Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.
 ```
 
+**Example 3:**
+
+```
+Input: num = "10", k = 2
+Output: "0"
+Explanation: Remove all the digits from the number and it is left with nothing which is 0.
+```
 
 ## 结语
 

leetcode/401-500/0402.Remove-K-Digits/Solution.go

@@ -1,5 +1,24 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(num string, k int) string {
+	n := len(num)
+	if n == k {
+		return "0"
+	}
+	stack := make([]byte, 0)
+	for idx := 0; idx < n; idx++ {
+		for k > 0 && len(stack) > 0 && stack[len(stack)-1] > num[idx] {
+			stack = stack[:len(stack)-1]
+			k--
+		}
+		stack = append(stack, num[idx])
+	}
+	stack = stack[:len(stack)-k]
+	i := 0
+	for ; i < len(stack) && stack[i] == '0'; i++ {
+	}
+	if i == len(stack) {
+		return "0"
+	}
+	return string(stack[i:])
 }

leetcode/401-500/0402.Remove-K-Digits/Solution_test.go

@@ -10,30 +10,31 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		inputs string
+		k      int
+		expect string
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", "1432219", 3, "1219"},
+		{"TestCase2", "10200", 1, "200"},
+		{"TestCase3", "101533485478947384734728478473847", 12, "13334734728478473847"},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.inputs, c.k)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v",
+					c.expect, got, c.inputs, c.k)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }