Create 0115-distinct-subsequences.kt

Author: a93a

kotlin/0115-distinct-subsequences.kt

@@ -0,0 +1,46 @@
+/*
+* DP bottom up
+*/
+class Solution {
+    fun numDistinct(s: String, t: String): Int {
+        val dp = Array(s.length + 1) { IntArray(t.length + 1) }
+
+        for (i in 0..s.length)
+            dp[i][t.length] = 1
+
+        for (i in s.length - 1 downTo 0) {
+            for (j in t.length - 1 downTo 0) {
+                if (s[i] == t[j])
+                    dp[i][j] += (dp[i + 1][j + 1] + dp[i + 1][j])
+                else
+                    dp[i][j] += dp[i + 1][j]
+            }
+        }
+
+        return dp[0][0]
+    }
+}
+
+/*
+* DFS + Memoization
+*/
+class Solution {
+    fun numDistinct(s: String, t: String): Int {
+        val memo = Array(s.length) { IntArray(t.length) { -1 } }
+
+        fun dfs(i: Int, j: Int): Int {
+            if (j == t.length) return 1
+            if (i == s.length) return 0      
+            if (memo[i][j] != -1) return memo[i][j]
+
+            if (s[i] == t[j])
+                memo[i][j] = dfs(i + 1, j + 1) + dfs(i + 1, j)
+            else
+                memo[i][j] = dfs(i + 1, j)
+            
+            return memo[i][j]
+        }
+
+        return dfs(0, 0)
+    }
+}