Distinct Subsequences
Written on October 21, 2015
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Given a string S and a string T, count the number of distinct subsequences of T in S. A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, "ACE" is a subsequence of "ABCDE" while "AEC" is not).
public class Solution {
/**
* @param S, T: Two string.
* @return: Count the number of distinct subsequences
*/
public int numDistinct(String S, String T) {
int len1 = S.length(), len2 = T.length();
int[][] count = new int[len1 + 1][len2 + 1];
for (int i = 0; i <= len1; i++) {
count[i][0] = 1;
}
for (int i = 1; i <= len1; i ++) {
for (int j = 1; j <= len2; j++) {
count[i][j] = count[i - 1][j];
if (S.charAt(i - 1) == T.charAt(j - 1)) {
count[i][j] += count[i - 1][j - 1];
}
}
}
return count[len1][len2];
}
}