Adding math

Author: Prashant Jain

src/in/knowledgegate/dsa/linkedlist/PascalTriangle.java

@@ -4,10 +4,18 @@
 import java.util.List;
 
 /**
- * Given an integer numRows, return the first numRows of Pascal's triangle. In
- * Pascal's triangle, each number is the sum of the two numbers directly above
- * it as shown.
- * <p>
+ * Given an integer numRows, return the first
+ * numRows of Pascal's triangle. In Pascal's
+ * triangle, each number is the sum of the two
+ * numbers directly above it as shown.
+ *
+ * 1
+ * 1 1
+ * 1 2 1
+ * 1 3 3 1
+ * 1 4 6 4 1
+ * 1 5 10 10 5 1
+ *
  * Example 1: Input: numRows = 5 Output:
  * [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]
  * <p>
@@ -17,22 +25,23 @@
  * Constraints: 1 <= numRows <= 30
  */
 public class PascalTriangle {
-    public List<List<Integer>> generate(int numRows) {
-        List<List<Integer>> result = new ArrayList<>();
-        List<Integer> prev = new ArrayList<>();
-        prev.add(1);
-        result.add(prev);
+  public List<List<Integer>> generate(int numRows) {
+    List<List<Integer>> result = new ArrayList<>();
+    List<Integer> prev = new ArrayList<>();
+    prev.add(1);
+    result.add(prev);
 
-        for (int i = 1; i < numRows; i++) {
-            List<Integer> curr = new ArrayList<>();
-            curr.add(1);
-            for (int j = 1; j < prev.size(); j++) {
-                curr.add(prev.get(j) + prev.get(j - 1));
-            }
-            curr.add(1);
-            result.add(curr);
-            prev = curr;
-        }
-        return result;
+    for (int i = 1; i < numRows; i++) {
+      List<Integer> curr = new ArrayList<>();
+      curr.add(1);
+      for (int j = 1; j < prev.size(); j++) {
+        int val = prev.get(j) + prev.get(j - 1);
+        curr.add(val);
+      }
+      curr.add(1);
+      result.add(curr);
+      prev = curr;
     }
+    return result;
+  }
 }

src/in/knowledgegate/dsa/math/PalindromeNumber.java

@@ -0,0 +1,49 @@
+package in.knowledgegate.dsa.math;
+
+/**
+ * Given an integer x, return true if x is
+ * palindrome integer.
+ *
+ * An integer is a palindrome when it reads
+ * the same backward as forward.
+ *
+ * For example, 121 is a palindrome while 123
+ * is not.
+ *
+ *
+ * Example 1:
+ * Input: x = 121
+ * Output: true
+ * Explanation: 121 reads as 121 from left to
+ * right and from right to left.
+ *
+ * Example 2:
+ * Input: x = -121
+ * Output: false
+ * Explanation: From left to right, it reads
+ * -121. From right to left, it becomes 121-.
+ * Therefore it is not a palindrome.
+ *
+ * Example 3:
+ * Input: x = 10
+ * Output: false
+ * Explanation: Reads 01 from right to left.
+ * Therefore it is not a palindrome.
+ *
+ *
+ * Constraints:
+ * -231 <= x <= 231 - 1
+ */
+public class PalindromeNumber {
+  public boolean isPalindrome(int x) {
+    if (x < 0) return false;
+    int rev = 0;
+    int temp = x;
+    while (temp > 0) {
+      int rem = temp % 10;
+      rev = rev * 10 + rem;
+      temp = temp / 10;
+    }
+    return x == rev;
+  }
+}

src/in/knowledgegate/dsa/strings/LongestCommonPrefix.java

@@ -1,29 +1,39 @@
 package in.knowledgegate.dsa.strings;
 
 /**
- * Write a function to find the longest common prefix string amongst an array of
- * strings. If there is no common prefix, return an empty string "".
+ * Write a function to find the longest common
+ * prefix string amongst an array of strings. If
+ * there is no common prefix, return an empty
+ * string "".
  * <p>
- * Example 1: Input: strs = ["flower","flow","flight"] Output: "fl"
+ * Example 1: Input: strs =
+ * ["flower","flow","flight"] Output: "fl"
  * <p>
- * Example 2: Input: strs = ["dog","racecar","car"] Output: "" Explanation:
- * There is no common prefix among the input strings.
+ * Example 2: Input: strs =
+ * ["dogasdfasdf","racecar","car"] Output: ""
+ * Explanation:
+ * There is no common prefix among the input
+ * strings.
  * <p>
  * <p>
- * Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i]
- * consists of only lower-case English letters.
+ * Constraints: 1 <= strs.length <= 200 0 <=
+ * strs[i].length <= 200 strs[i] consists of only
+ * lower-case English letters.
  */
 public class LongestCommonPrefix {
-    public String longestCommonPrefix(String[] strs) {
-        String result = "";
-        for (int i = 0; i < strs[0].length(); i++) {
-            for (int j = 1; j < strs.length; j++) {
-                if (strs[j].length() <= i || strs[0].charAt(i) != strs[j].charAt(i)) {
-                    return result;
-                }
-            }
-            result += strs[0].charAt(i);
+  public String longestCommonPrefix(String[] strs) {
+    String result = "";
+    for (int i = 0; i < strs[0].length(); i++) {
+      char finding = strs[0].charAt(i);
+      for (int j = 1; j < strs.length; j++) {
+        if (strs[j].length() <= i ||
+           finding != strs[j].charAt(i)) {
+            return result;
         }
-        return result;
+      }
+      result += finding;
     }
+
+    return result;
+  }
 }