Description
Distinct Subsequences
HardGiven two strings s and t, return the number of distinct subsequences of s which equals t.
The test cases are generated so that the answer fits on a 32-bit signed integer.
Example 1:
Input: s = "rabbbit", t = "rabbit" Output: 3 Explanation: As shown below, there are 3 ways you can generate "rabbit" from s.rabbbitrabbbitrabbbit
Example 2:
Input: s = "babgbag", t = "bag" Output: 5 Explanation: As shown below, there are 5 ways you can generate "bag" from s.babgbagbabgbagbabgbagbabgbagbabgbag
Constraints:
1 <= s.length, t.length <= 1000sandtconsist of English letters.
Solutions
Crazy 1-dimension dp solution, seems like magic to me.
Language: javascript()DONE
CPU Performance57.23%
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Memory Performance72.06%
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/**
* @param {string} s
* @param {string} t
* @return {number}
*/
var numDistinct = function(s, t) {
const dp = Array(t.length + 1).fill(0);
dp[0] = 1;
for (const char of s) {
for (let j = t.length - 1; j >= 0; j--) {
if (char === t[j]) {
dp[j + 1] += dp[j];
}
}
}
return dp[t.length];
};