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A character is unique in string S
if it occurs exactly once in it.
For example, in string S = "LETTER"
, the only unique characters are "L"
and "R"
.
Let's define UNIQ(S)
as the number of unique characters in string S
.
For example, UNIQ("LETTER") = 2
.
Given a string S
with only uppercases, calculate the sum of UNIQ(substring)
over all non-empty substrings of S
.
If there are two or more equal substrings at different positions in S
, we consider them different.
Since the answer can be very large, return the answer modulo 10 ^ 9 + 7
.
Example 1:
Input: "ABC" Output: 10 Explanation: All possible substrings are: "A","B","C","AB","BC" and "ABC". Evey substring is composed with only unique letters. Sum of lengths of all substring is 1 + 1 + 1 + 2 + 2 + 3 = 10
Example 2:
Input: "ABA" Output: 8 Explanation: The same as example 1, except uni("ABA") = 1.
Note: 0 <= S.length <= 10000
.
如果一个字符在字符串 S
中有且仅有出现一次,那么我们称其为独特字符。
例如,在字符串 S = "LETTER"
中,"L"
和 "R"
可以被称为独特字符。
我们再定义 UNIQ(S)
作为字符串 S
中独特字符的个数。
那么,在 S = "LETTER"
中, UNIQ("LETTER") = 2
。
对于给定字符串 S
,计算其所有非空子串的独特字符的个数,即 UNIQ(substring)
。
如果出现两个或者多个相同的子串,将其认为是不同的两个子串。
考虑到答案可能会非常大,规定返回格式为:结果 mod 10 ^ 9 + 7
。
示例 1:
输入: "ABC" 输出: 10 解释: 所有可能的子串为:"A","B","C","AB","BC" 和 "ABC"。 其中,每一个子串都由独特字符构成。 所以其长度总和为:1 + 1 + 1 + 2 + 2 + 3 = 10
示例 2:
输入: "ABA" 输出: 8 解释: 除了子串 UNIQ('ABA') = 1,其余与示例1相同。
说明: 0 <= S.length <= 10000
。
1 class Solution { 2 func uniqueLetterString(_ S: String) -> Int { 3 var index:[[Int]] = [[Int]](repeating:[Int](repeating:-1,count:2),count:26) 4 var res:Int = 0 5 var N:Int = S.count 6 var mod:Int = Int(pow(10.0,9.0)) + 7 7 for i in 0..<N 8 { 9 var c:Int = S[i].ascii - 65 10 res = (res + (i - index[c][1]) * (index[c][1] - index[c][0]) % mod) % mod 11 index[c] = [index[c][1], i] 12 } 13 for c in 0..<26 14 { 15 res = (res + (N - index[c][1]) * (index[c][1] - index[c][0]) % mod) % mod 16 } 17 return res 18 } 19 } 20 21 //String扩展 22 extension String { 23 //subscript函数可以检索数组中的值 24 //直接按照索引方式截取指定索引的字符 25 subscript (_ i: Int) -> Character { 26 //读取字符 27 get {return self[index(startIndex, offsetBy: i)]} 28 } 29 } 30 31 //Character扩展 32 extension Character 33 { 34 //Character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 ?? 0) 38 } 39 } 40 }