标签：tst size mat char int fonts xpl sequence bing
Given two strings S and T. Count the number of distinct subsequences of S which equals T.
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)
Example 1:
Input: S = "rabbbit", T = "rabbit"
Output: 3
Explanation: You could remove any ‘b‘ in S, so there are 3 ways to get T.
Example 2:
Input: S = "abcd", T = ""
Output: 1
Explanation: There is only 1 way to get T - remove all chars in S.
Do it in O(n^2??) time and O(n) memory.
O(n^2??) memory is also acceptable if you do not know how to optimize memory.
public int numDistinct(String S, String T) {
if (S == null || T == null) {
return 0;
}
int[][] nums = new int[S.length() + 1][T.length() + 1];
for (int i = 0; i <= S.length(); i++) {
nums[i][0] = 1;
}
for (int i = 1; i <= S.length(); i++) {
for (int j = 1; j <= T.length(); j++) {
nums[i][j] = nums[i - 1][j];
if (S.charAt(i - 1) == T.charAt(j - 1)) {
nums[i][j] += nums[i - 1][j - 1];
}
}
}
return nums[S.length()][T.length()];
}
标签：tst size mat char int fonts xpl sequence bing
原文地址：https://www.cnblogs.com/FLAGyuri/p/12078446.html
