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Solution.cs
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65 lines (60 loc) · 2.13 KB
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public class Solution
{
public int FindTheLongestSubstring(string s)
{
// a: 'a' - 'a' = 0
// e: 'e' - 'a' = 4
// i: 'i' - 'a' = 8
// o: 'o' - 'a' = 14
//u: 'u' - 'a' = 20
//=> vowelsBitMask = 100000100000100010001 -> 1065233 (int)
// u o i e a
int vowelsBitMask = 1065233;
// for each s[i], we represent the character as a bitmask.
// s[i] = 'a' => b[i] = 00..01 (26 bits)
// s[i] = 'b' => b[i] = 00..10 (26 bits)
// ....
// s[i] = 'z' => b[i] = 10...0 (26 bits)
// b[i] = 1 << (s[i] - 'a')
// dp[i] = b[0] ^ b[1] ^...^b[i]
int[] dp = new int[s.Length];
Array.Fill(dp, 0);
dp[0] = 1 << (s[0] - 'a');
for (int i = 1; i < s.Length; i++)
{
dp[i] = dp[i - 1] ^ (1 << (s[i] - 'a'));
}
// s = "aabbe", n = s.Length = 5
// dp = [00001,00000,00010,00000,10000]
// "a" : 00001
// "aa" : 00000
// "aab" : 00010
// "aabb" : 00000
// "aabbe" : 10000
// vowelsBitMask = "100000100000100010001"
// 1. len = 5
// start = 0, end = 4, substring = "aabbe"
// bitMask = start == 0 ? dp[end] : dp[start - 1] ^ dp[end]
//. = dp[4] = 10000
// bitMask & vowelsBitMask = 10000 & 100000100000100010001 = 10000 != 0
// 2. len = 4
// start = 0, end = 3, substring = "aabb"
// bitMask = start == 0 ? dp[end] : dp[start - 1] ^ dp[end]
//. = dp[3] = 00000
// bitMask & vowelsBitMask = 00000 & 100000100000100010001 = 00000 == 0
// => ans = len = 4
for (int len = s.Length; len > 0; len--)
{
for (int start = 0; start + len - 1 < s.Length; start++)
{
int end = start + len - 1;
var bitMask = start == 0 ? dp[end] : dp[start - 1] ^ dp[end];
if ((bitMask & vowelsBitMask) == 0)
{
return len;
}
}
}
return 0;
}
}