LeetCode 115. Distinct Subsequences

#include <string>
#include <vector>
#include <iostream>
using namespace std;


// for example, S = "ABCDE", P = "AEC" --> return 1
// for example: S = "rabbbit", P = "rabbit" --> return 3.
int distinctSubsequences(string s, string t) {
  int m = t.size(), n = s.size();
  vector< vector<int> > dp(m + 1, vector<int>(n+1, 0));
  for(int i = 0; i <= m; ++i) {
    for(int j = 0; j <= n; ++j) {
      if(i == 0) dp[0][j] = 1; // empty string can always match.
      else dp[i][j] = (t[i-1] == s[j-1]) * dp[i-1][j-1] + dp[i][j-1];
    }
  }
  return dp[m][n];
}

int main(void) {
  cout << distinctSubsequences("AABC", "AC") << endl;
}