Documented JS solutions for problem 97

Author: imaginate

javascript/97-Interleaving-String.js

@@ -1,3 +1,9 @@
+//////////////////////////////////////////////////////////////////////////////
+// 1D Dynamic Programming
+// Time: O(n*m)
+// Space: O(m)
+//////////////////////////////////////////////////////////////////////////////
+
 /**
  * @param {string} s1
  * @param {string} s2
@@ -21,33 +27,27 @@ function isInterleave(s1, s2, s3) {
         );
     }
 
-    const seen = new Array(l1 + 1).fill()
-        .map(() => new Array(l2 + 1));
-    return checkStrings();
+    const seen = new Array(l2 + 1);
+    seen[l2] = true;
 
-    /**
-     * @param {number=} i = `0`
-     * @param {number=} j = `0`
-     * @param {number=} k = `0`
-     * @return {boolean}
-     */
-    function checkStrings(i = 0, j = 0, k = 0) {
-        return k === l3 || (
-            seen[i][j] !== undefined
-                ? seen[i][j]
-                : seen[i][j] = (
-                    i < l1
-                    && s1[i] === s3[k]
-                    && checkStrings(i + 1, j, k + 1)
-                ) || (
-                    j < l2
-                    && s2[j] === s3[k]
-                    && checkStrings(i, j + 1, k + 1)
-                )
-        );
+    for (let i = l2 - 1; i >= 0; --i) {
+        seen[i] = seen[i + 1] && s2[i] === s3[l1 + i];
     }
+    for (let i = l1 - 1; i >= 0; --i) {
+        for (let j = l2; j >= 0; --j) {
+            seen[j] = (seen[j] && s1[i] === s3[i + j])
+                || (j !== l2 && seen[j + 1] && s2[j] === s3[i + j]);
+        }
+    }
+    return seen[0];
 }
 
+//////////////////////////////////////////////////////////////////////////////
+// 2D Dynamic Programming
+// Time: O(n*m)
+// Space: O(n*m)
+//////////////////////////////////////////////////////////////////////////////
+
 /**
  * @param {string} s1
  * @param {string} s2
@@ -90,6 +90,12 @@ function isInterleave(s1, s2, s3) {
     return seen[0][0];
 }
 
+//////////////////////////////////////////////////////////////////////////////
+// Depth First Search Recursion With Memoization
+// Time: O(n*m)
+// Space: O(n*m)
+//////////////////////////////////////////////////////////////////////////////
+
 /**
  * @param {string} s1
  * @param {string} s2
@@ -113,17 +119,29 @@ function isInterleave(s1, s2, s3) {
         );
     }
 
-    const seen = new Array(l2 + 1);
-    seen[l2] = true;
+    const seen = new Array(l1 + 1).fill()
+        .map(() => new Array(l2 + 1));
+    return checkStrings();
 
-    for (let i = l2 - 1; i >= 0; --i) {
-        seen[i] = seen[i + 1] && s2[i] === s3[l1 + i];
-    }
-    for (let i = l1 - 1; i >= 0; --i) {
-        for (let j = l2; j >= 0; --j) {
-            seen[j] = (seen[j] && s1[i] === s3[i + j])
-                || (j !== l2 && seen[j + 1] && s2[j] === s3[i + j]);
-        }
+    /**
+     * @param {number=} i = `0`
+     * @param {number=} j = `0`
+     * @param {number=} k = `0`
+     * @return {boolean}
+     */
+    function checkStrings(i = 0, j = 0, k = 0) {
+        return k === l3 || (
+            seen[i][j] !== undefined
+                ? seen[i][j]
+                : seen[i][j] = (
+                    i < l1
+                    && s1[i] === s3[k]
+                    && checkStrings(i + 1, j, k + 1)
+                ) || (
+                    j < l2
+                    && s2[j] === s3[k]
+                    && checkStrings(i, j + 1, k + 1)
+                )
+        );
     }
-    return seen[0];
 }