We are given that the string "abc"
is valid.
From any valid string V
, we may split V
into two pieces X
and Y
such that X + Y
(X
concatenated with Y
) is equal to V
. (X
or Y
may be empty.) Then, X + "abc" + Y
is also valid.
If for example S = "abc"
, then examples of valid strings are: "abc", "aabcbc", "abcabc", "abcabcababcc"
. Examples of invalid strings are: "abccba"
, "ab"
, "cababc"
, "bac"
.
Return true
if and only if the given string S
is valid.
Example 1:
Input: "aabcbc"
Output: true
Explanation:
We start with the valid string "abc".
Then we can insert another "abc" between "a" and "bc", resulting in "a" + "abc" + "bc" which is "aabcbc".
Example 2:
Input: "abcabcababcc"
Output: true
Explanation:
"abcabcabc" is valid after consecutive insertings of "abc".
Then we can insert "abc" before the last letter, resulting in "abcabcab" + "abc" + "c" which is "abcabcababcc".
Example 3:
Input: "abccba"
Output: false
Example 4:
Input: "cababc"
Output: false
Note:
1 <= S.length <= 20000
S[i]
is'a'
,'b'
, or'c'
给定有效字符串 "abc"
。
对于任何有效的字符串 V
,我们可以将 V
分成两个部分 X
和 Y
,使得 X + Y
(X
与 Y
连接)等于 V
。(X
或 Y
可以为空。)那么,X + "abc" + Y
也同样是有效的。
例如,如果 S = "abc"
,则有效字符串的示例是:"abc"
,"aabcbc"
,"abcabc"
,"abcabcababcc"
。无效字符串的示例是:"abccba"
,"ab"
,"cababc"
,"bac"
。
如果给定字符串 S
有效,则返回 true
;否则,返回 false
。
示例 1:
输入:"aabcbc" 输出:true 解释: 从有效字符串 "abc" 开始。 然后我们可以在 "a" 和 "bc" 之间插入另一个 "abc",产生 "a" + "abc" + "bc",即 "aabcbc"。
示例 2:
输入:"abcabcababcc" 输出:true 解释: "abcabcabc" 是有效的,它可以视作在原串后连续插入 "abc"。 然后我们可以在最后一个字母之前插入 "abc",产生 "abcabcab" + "abc" + "c",即 "abcabcababcc"。
示例 3:
输入:"abccba" 输出:false
示例 4:
输入:"cababc" 输出:false
提示:
1 <= S.length <= 20000
S[i]
为'a'
、'b'
、或'c'
1 class Solution { 2 func isValid(_ S: String) -> Bool { 3 var n:Int = S.count 4 var arr:[Character] = Array(S) 5 var h:[Int] = [Int](repeating:0,count:3) 6 for i in 0..<n 7 { 8 h[arr[i].ascii - 97] += 1 9 } 10 if !S.contains("abc") 11 { 12 return false 13 } 14 if h[0] != h[1] || h[1] != h[2] 15 { 16 return false 17 } 18 var cc:[Int] = [Int](repeating:0,count:3) 19 for i in 0..<n 20 { 21 cc[arr[i].ascii - 97] += 1 22 if cc[0] < cc[1] || cc[1] < cc[2] 23 { 24 return false 25 } 26 } 27 return true 28 } 29 } 30 31 //Character扩展 32 extension Character 33 { 34 //转ASCII整数值(定义小写为整数值) 35 var ascii: Int { 36 get { 37 return Int(self.unicodeScalars.first!.value) 38 } 39 } 40 }