LeetCode-in-Java
3298. Count Substrings That Can Be Rearranged to Contain a String II
Hard
You are given two strings word1 and word2.
A string x is called valid if x can be rearranged to have word2 as a prefix.
Return the total number of valid substrings of word1.
Note that the memory limits in this problem are smaller than usual, so you must implement a solution with a linear runtime complexity.
Example 1:
Input: word1 = “bcca”, word2 = “abc”
Output: 1
Explanation:
The only valid substring is "bcca" which can be rearranged to "abcc" having "abc" as a prefix.
Example 2:
Input: word1 = “abcabc”, word2 = “abc”
Output: 10
Explanation:
All the substrings except substrings of size 1 and size 2 are valid.
Example 3:
Input: word1 = “abcabc”, word2 = “aaabc”
Output: 0
Constraints:
1 <= word1.length <= 1061 <= word2.length <= 104word1andword2consist only of lowercase English letters.
Solution
public class Solution {
public long validSubstringCount(String word1, String word2) {
char[] ar = word1.toCharArray();
int n = ar.length;
char[] temp = word2.toCharArray();
int[] f = new int[26];
for (char i : temp) {
f[i - 97]++;
}
long ans = 0;
int needed = temp.length;
int beg = 0;
int end = 0;
while (end < n) {
if (f[ar[end] - 97]-- > 0) {
needed--;
}
while (needed == 0) {
// All substrings from [beg, i], where end <= i < n are valid
ans += n - end;
// Shrink
if (f[ar[beg++] - 97]++ == 0) {
needed++;
}
}
end++;
}
return ans;
}
}