Added more problems

Author: Prashant Jain

src/in/knowledgegate/dsa/binarysearch/problems/ArrangingCoins.java

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+package in.knowledgegate.dsa.binarysearch.problems;
+
+/**
+ * You have n coins and you want to build a staircase
+ * with these coins. The staircase consists of k
+ * rows where the ith row has exactly i coins.
+ * The last row of the staircase may be incomplete.
+ *
+ * Given the integer n, return the number of
+ * complete rows of the staircase you will build.
+ *
+ * Example 1:
+ * Input: n = 5
+ * Output: 2
+ * Explanation: Because the 3rd row is incomplete,
+ * we return 2.
+ *
+ * Example 2:
+ * Input: n = 8
+ * Output: 3
+ * Explanation: Because the 4th row is incomplete,
+ * we return 3.
+ *
+ * Constraints:
+ * 1 <= n <= 231 - 1
+ */
+public class ArrangingCoins {
+    public static void main(String[] args) {
+        ArrangingCoins arrange =
+            new ArrangingCoins();
+        System.out.println("No of stairs:"
+            + arrange.arrangeCoins(5));
+    }
+
+    private int arrangeCoins(int n) {
+        int begin = 0;
+        int end = n;
+        while (begin <= end) {
+            int mid = (begin + end)/2;
+            int coinsUsed = (mid * (mid + 1)) / 2;
+            if (coinsUsed == n) return mid;
+            if (coinsUsed < n) {
+                begin = mid + 1;
+            } else {
+                end = mid - 1;
+            }
+        }
+        return end;
+    }
+}

src/in/knowledgegate/dsa/bitmanipulation/ConvertNumberToHexadecimal.java

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+package in.knowledgegate.dsa.bitmanipulation;
+
+/**
+ * Given an integer num, return a string
+ * representing its hexadecimal representation.
+ * For negative integers, two’s complement method
+ * is used.
+ *
+ * All the letters in the answer string should be
+ * lowercase characters, and there should not be
+ * any leading zeros in the answer except for the
+ * zero itself.
+ *
+ * Note: You are not allowed to use any built-in
+ * library method to directly solve this problem.
+ *
+ *
+ * Example 1:
+ * Input: num = 26
+ * Output: "1a"
+ *
+ * Example 2:
+ * Input: num = -1
+ * Output: "ffffffff"
+ *
+ * Constraints:
+ * -231 <= num <= 231 - 1
+ */
+public class ConvertNumberToHexadecimal {
+    public static void main(String[] args) {
+        ConvertNumberToHexadecimal converter =
+            new ConvertNumberToHexadecimal();
+        System.out.println("Hex num is: "
+            + converter.toHex(26));
+    }
+
+    public String toHex(int num) {
+        char[] mapping = new char[]{'0', '1', '2'
+            , '3', '4', '5', '6', '7', '8', '9',
+            'a', 'b', 'c', 'd', 'e', 'f'};
+        if (num == 0) return "0";
+        StringBuilder result = new StringBuilder();
+        while (num > 0) {
+            int endBits = num & 15;
+            result.insert(0, mapping[endBits]);
+            num = num >> 4;
+        }
+        return result.toString();
+    }
+}