[toychip] Week 03 solutions (#1297)

* valid-palindrome solution

* maximum-subarray solution

* blank lint

Author: toychip

maximum-subarray/toychip.java

@@ -0,0 +1,12 @@
+class Solution {
+    public int maxSubArray(int[] nums) {
+        int maxSum = nums[0];
+        int currentSum = nums[0];
+
+        for (int i = 1; i < nums.length; i++) {
+            currentSum = Math.max(nums[i], currentSum + nums[i]);
+            maxSum = Math.max(maxSum, currentSum);
+        }
+        return maxSum;
+    }
+}

valid-palindrome/toychip.java

@@ -0,0 +1,33 @@
+class Solution {
+    public boolean isPalindrome(String s) {
+        char[] charArray = s.toCharArray();
+        StringBuilder stringBuilder = new StringBuilder();
+
+        for (char c : charArray) {
+            if (Character.isLetterOrDigit(c)) {
+                stringBuilder.append(c);
+            }
+        }
+
+        String validChars = stringBuilder.toString();
+
+        char[] validArray = validChars.toCharArray();
+        char[] reversArray = new char[validArray.length];
+
+        for (int i = 0; i < validArray.length; i++) {
+            validArray[i] = Character.toLowerCase(validArray[i]);
+            reversArray[i] = Character.toLowerCase(reversArray[i]);
+        }
+
+        for (int i = 0; i < validArray.length; i++) {
+            reversArray[validArray.length - 1 - i] = validArray[i];
+        }
+
+        for (int i = 0; i < validArray.length; i++) {
+            if (reversArray[i] != validArray[i]) {
+                return false;
+            }
+        }
+        return true;
+    }
+}