题目：

题解：

int numDistinct(char* s, char* t) {int m = strlen(s), n = strlen(t);if (m < n) {return 0;}unsigned long long dp[m + 1][n + 1];memset(dp, 0, sizeof(dp));for (int i = 0; i <= m; i++) {dp[i][n] = 1;}for (int i = m - 1; i >= 0; i--) {char sChar = s[i];for (int j = n - 1; j >= 0; j--) {char tChar = t[j];if (sChar == tChar) {dp[i][j] = dp[i + 1][j + 1] + dp[i + 1][j];} else {dp[i][j] = dp[i + 1][j];}}}return dp[0][0];
}