规范格式

leetcode/0880.Decoded-String-at-Index/880. Decoded String at Index.go

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+package leetcode
+
+func isLetter(char byte) bool {
+	if char >= 'a' && char <= 'z' {
+		return true
+	}
+	return false
+}
+
+func decodeAtIndex(S string, K int) string {
+	length := 0
+	for i := 0; i < len(S); i++ {
+		if isLetter(S[i]) {
+			length++
+			if length == K {
+				return string(S[i])
+			}
+		} else {
+			if length*int(S[i]-'0') >= K {
+				if K%length != 0 {
+					return decodeAtIndex(S[:i], K%length)
+				}
+				return decodeAtIndex(S[:i], length)
+			}
+			length *= int(S[i] - '0')
+		}
+	}
+	return ""
+}

leetcode/0880.Decoded-String-at-Index/880. Decoded String at Index_test.go

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+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question880 struct {
+	para880
+	ans880
+}
+
+// para 是参数
+// one 代表第一个参数
+type para880 struct {
+	s string
+	k int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans880 struct {
+	one string
+}
+
+func Test_Problem880(t *testing.T) {
+
+	qs := []question880{
+
+		question880{
+			para880{"aw4eguc6cs", 41},
+			ans880{"a"},
+		},
+
+		question880{
+			para880{"vk6u5xhq9v", 554},
+			ans880{"h"},
+		},
+
+		question880{
+			para880{"leet2code3", 10},
+			ans880{"o"},
+		},
+
+		question880{
+			para880{"ha22", 5},
+			ans880{"h"},
+		},
+
+		question880{
+			para880{"a2345678999999999999999", 1},
+			ans880{"a"},
+		},
+
+		question880{
+			para880{"y959q969u3hb22odq595", 222280369},
+			ans880{"q"},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 880------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans880, q.para880
+		fmt.Printf("【input】:%v       【output】:%v\n", p, decodeAtIndex(p.s, p.k))
+	}
+	fmt.Printf("\n\n\n")
+}

leetcode/0880.Decoded-String-at-Index/README.md

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+# [880. Decoded String at Index](https://leetcode.com/problems/decoded-string-at-index/)
+
+## 题目
+
+An encoded string S is given.  To find and write the decoded string to a tape, the encoded string is read one character at a time and the following steps are taken:
+
+If the character read is a letter, that letter is written onto the tape.
+If the character read is a digit (say d), the entire current tape is repeatedly written d-1 more times in total.
+Now for some encoded string S, and an index K, find and return the K-th letter (1 indexed) in the decoded string.
+
+ 
+
+Example 1:
+
+```c
+Input: S = "leet2code3", K = 10
+Output: "o"
+Explanation: 
+The decoded string is "leetleetcodeleetleetcodeleetleetcode".
+The 10th letter in the string is "o".
+```
+
+Example 2:
+
+```c
+Input: S = "ha22", K = 5
+Output: "h"
+Explanation: 
+The decoded string is "hahahaha".  The 5th letter is "h".
+```
+
+Example 3:
+
+```c
+Input: S = "a2345678999999999999999", K = 1
+Output: "a"
+Explanation: 
+The decoded string is "a" repeated 8301530446056247680 times.  The 1st letter is "a".
+```
+
+Note:
+
+1. 2 <= S.length <= 100
+2. S will only contain lowercase letters and digits 2 through 9.
+3. S starts with a letter.
+4. 1 <= K <= 10^9
+5. The decoded string is guaranteed to have less than 2^63 letters.
+
+## 题目大意
+
+给定一个编码字符串 S。为了找出解码字符串并将其写入磁带，从编码字符串中每次读取一个字符，并采取以下步骤：  
+
+- 如果所读的字符是字母，则将该字母写在磁带上。
+- 如果所读的字符是数字（例如 d），则整个当前磁带总共会被重复写 d-1 次。   
+  
+现在，对于给定的编码字符串 S 和索引 K，查找并返回解码字符串中的第 K 个字母。
+
+
+## 解题思路
+
+按照题意，扫描字符串扫到数字的时候，开始重复字符串，这里可以用递归。注意在重复字符串的时候到第 K 个字符的时候就可以返回了，不要等所有字符都扩展完成，这样会超时。d 有可能超大。