Correct Space Complexity and Optimized Solution for LeetCode 383: Ransom Note

Ransom Note - Leetcode 383/Ransom Note - Leetcode 383.cpp

@@ -5,19 +5,23 @@ using namespace std;
 class Solution {
 public:
     bool canConstruct(string ransomNote, string magazine) {
-        unordered_map<char, int> counter;
-        
-        for (char c : magazine) {
-            counter[c]++;
+        unordered_map<char, int> hashmap;
+
+        for (char ch : magazine) {
+            hashmap[ch]++;
         }
-
-        for (char c : ransomNote) {
-            if (counter[c] == 0) {
+
+        for (char ch : ransomNote) {
+            if (hashmap[ch] > 0) {
+                hashmap[ch]--;
+            } else {
                 return false;
             }
-            counter[c]--;
         }
-        
+
         return true;
     }
 };
+
+// Time Complexity: O(m + n)  -> m = length of ransomNote, n = length of magazine
+// Space Complexity: O(n)     -> we're using an unordered_map

Ransom Note - Leetcode 383/Ransom Note - Leetcode 383.java

@@ -1,20 +1,24 @@
 import java.util.HashMap;
 
-public class Solution {
+class Solution {
     public boolean canConstruct(String ransomNote, String magazine) {
-        HashMap<Character, Integer> counter = new HashMap<>();
+        HashMap<Character, Integer> hashmap = new HashMap<>(); 
 
-        for (char c : magazine.toCharArray()) {
-            counter.put(c, counter.getOrDefault(c, 0) + 1);
+        for (char ch : magazine.toCharArray()) {
+            hashmap.put(ch, hashmap.getOrDefault(ch, 0) + 1);
         }
-
-        for (char c : ransomNote.toCharArray()) {
-            if (!counter.containsKey(c) || counter.get(c) == 0) {
+
+        for (char ch : ransomNote.toCharArray()) {
+            if (hashmap.getOrDefault(ch, 0) > 0) {
+                hashmap.put(ch, hashmap.get(ch) - 1);
+            } else {
                 return false;
             }
-            counter.put(c, counter.get(c) - 1);
         }
 
         return true;
     }
 }
+
+// Time Complexity: O(m + n)  -> m = len(ransomNote), n = len(magazine)
+// Space Complexity: O(n)     -> we're using a hashmap

Ransom Note - Leetcode 383/Ransom Note - Leetcode 383.js

@@ -1,16 +1,20 @@
-function canConstruct(ransomNote, magazine) {
-    const counter = {};
-    
-    for (const c of magazine) {
-        counter[c] = (counter[c] || 0) + 1;
+var canConstruct = function(ransomNote, magazine) {
+    let hashmap = {}; 
+
+    for (let ch of magazine) {
+        hashmap[ch] = (hashmap[ch] || 0) + 1;
     }
-
-    for (const c of ransomNote) {
-        if (!counter[c] || counter[c] === 0) {
+
+    for (let ch of ransomNote) {
+        if (hashmap[ch] > 0) {
+            hashmap[ch]--;
+        } else {
             return false;
         }
-        counter[c]--;
     }
-    
+
     return true;
-}
+};
+
+// Time Complexity: O(m + n)  -> m = length of ransomNote, n = length of magazine
+// Space Complexity: O(n)     -> we're using a hashmap

Ransom Note - Leetcode 383/Ransom Note - Leetcode 383.py

@@ -1,22 +1,13 @@
 class Solution:
     def canConstruct(self, ransomNote: str, magazine: str) -> bool:
-        counter = {}
+        hashmap = Counter(magazine) # TC for Counter is O(n)
 
-        for c in magazine:
-            if c in counter:
-                counter[c] += 1
+        for ch in ransomNote:
+            if hashmap[ch] > 0:
+                hashmap[ch]-=1
             else:
-                counter[c] = 1
-
-        for c in ransomNote:
-            if c not in counter:
                 return False
-            elif counter[c] == 1:
-                del counter[c]
-            else:
-                counter[c] -= 1
-
         return True
 
-# Time Complexity: O(m + n)
-# Space Complexity: O(1)
+# Time Complexity: O(m + n)  -> m = len(ransomNote), n = len(magazine)
+# Space Complexity: O(n)     -> we're using a hashmap