940 added

Author: aQuaYi

Algorithms/0940.distinct-subsequences-ii/README.md

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+# [940. Distinct Subsequences II](https://leetcode.com/problems/distinct-subsequences-ii/)
+
+Given a string S, count the number of distinct, non-empty subsequences of S .
+
+Since the result may be large, return the answer modulo 10^9 + 7.
+
+Example 1:
+
+```text
+Input: "abc"
+Output: 7
+Explanation: The 7 distinct subsequences are "a", "b", "c", "ab", "ac", "bc", and "abc".
+```
+
+Example 2:
+
+```text
+Input: "aba"
+Output: 6
+Explanation: The 6 distinct subsequences are "a", "b", "ab", "ba", "aa" and "aba".
+```
+
+Example 3:
+
+```text
+Input: "aaa"
+Output: 3
+Explanation: The 3 distinct subsequences are "a", "aa" and "aaa".
+```
+
+Note:
+
+1. `S contains only lowercase letters.`
+1. `1 <= S.length <= 2000`

Algorithms/0940.distinct-subsequences-ii/distinct-subsequences-ii.go

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+package problem0940
+
+func distinctSubseqII(S string) int {
+
+	return 0
+}

Algorithms/0940.distinct-subsequences-ii/distinct-subsequences-ii_test.go

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+package problem0940
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// tcs is testcase slice
+var tcs = []struct {
+	S   string
+	ans int
+}{
+
+	{
+		"abc",
+		7,
+	},
+
+	{
+		"aba",
+		6,
+	},
+
+	{
+		"aaa",
+		3,
+	},
+
+	// 可以有多个 testcase
+}
+
+func Test_distinctSubseqII(t *testing.T) {
+	ast := assert.New(t)
+
+	for _, tc := range tcs {
+		ast.Equal(tc.ans, distinctSubseqII(tc.S), "输入:%v", tc)
+	}
+}
+
+func Benchmark_distinctSubseqII(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range tcs {
+			distinctSubseqII(tc.S)
+		}
+	}
+}