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package g0901_1000.s0940_distinct_subsequences_ii;
// #Hard #String #Dynamic_Programming #2022_03_30_Time_2_ms_(99.41%)_Space_40.3_MB_(98.22%)
public class Solution {
public int distinctSubseqII(String str) {
int m = (int) (1e9) + 7;
int prev = 1;
int[] subseqAtPrevIndexOfMyLastOcc = new int[26];
for (int i = 1; i <= str.length(); i++) {
int crntStrIdx = i - 1;
int subtract = subseqAtPrevIndexOfMyLastOcc[str.charAt(crntStrIdx) - 'a'];
int curr = (2 * prev) % m;
curr = (curr + m - subtract) % m;
subseqAtPrevIndexOfMyLastOcc[str.charAt(crntStrIdx) - 'a'] = prev;
prev = curr;
}
return prev - 1;
}
}