[Hoonjichoi] WEEK 02 solutions

climbing-stairs/hoonjichoi1.java

@@ -0,0 +1,24 @@
+
+/*
+f(45) = f(44) + f(43)
+f(44) = f(43) + f(42)
+.
+.
+.
+f(3) = f(2) + f(1)
+f(2) = 2
+f(1) = 1
+*/
+class Solution {
+    public int climbStairs(int n) {
+        if (n <= 2) return n;
+
+        int prev = 1, cur = 2;
+        for (int i = 2; i < n ; i++) {
+            int temp = cur;
+            cur += prev;
+            prev = temp;
+        }     
+        return cur;
+    }
+}

valid-anagram/hoonjichoi1.java

@@ -0,0 +1,33 @@
+import java.util.HashMap;
+
+public class hoonjichoi1 {
+    public boolean isAnagram(String s, String t) {
+        if (s.equals(t))
+            return true;
+        if (s.length() != t.length())
+            return false;
+
+        HashMap<Character, Integer> map = new HashMap<>();
+
+        for (int i = 0; i < s.length(); i++) {
+            Character c = s.charAt(i);
+            map.put(c, map.getOrDefault(c, 0) + 1);
+        }
+
+        for (int j = 0; j < t.length(); j++) {
+            Character c = t.charAt(j);
+            if (!map.containsKey(c) || map.get(c) <= 0) {
+                return false;
+            }
+
+            map.put(c, map.get(c) - 1);
+        }
+
+        for (Integer i : map.values()) {
+            if (i < 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+}