pow x^n : done

Author: rampatra

src/main/java/com/leetcode/arrays/binarysearch/PowXN.java

@@ -0,0 +1,85 @@
+package com.leetcode.arrays.binarysearch;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Level: Medium
+ * Link: https://leetcode.com/problems/powx-n/
+ * Description:
+ * Implement pow(x, n), which calculates x raised to the power n (x^n).
+ * <p>
+ * Example 1:
+ * Input: 2.00000, 10
+ * Output: 1024.00000
+ * <p>
+ * Example 2:
+ * Input: 2.10000, 3
+ * Output: 9.26100
+ * <p>
+ * Example 3:
+ * Input: 2.00000, -2
+ * Output: 0.25000
+ * Explanation: 2^-2 = 1/22 = 1/4 = 0.25
+ * <p>
+ * Note:
+ * -100.0 < x < 100.0
+ * n is a 32-bit signed integer, within the range [−231, 231 − 1]
+ *
+ * @author rampatra
+ * @since 2019-08-19
+ */
+public class PowXN {
+
+    /**
+     * In this approach we iterate n times and keep multiplying x with x.
+     * Runtime: <a href="https://leetcode.com/submissions/detail/253075786/">Time limit exceeded</a>.
+     *
+     * @param x
+     * @param n
+     * @return
+     */
+    public static double myPowNaive(double x, int n) {
+        if (n == 0) {
+            return 1;
+        }
+        double res = x;
+        int absN = Math.abs(n);
+        for (int i = 1; i < absN; i++) {
+            res *= x;
+        }
+        return n < 0 ? 1 / res : res;
+    }
+
+
+    /**
+     * In this approach, we iterate log n times. We omit half of n each time. When n is odd, we store whatever product
+     * we have calculated so far in the final result.
+     * <p>
+     * Runtime: <a href="https://leetcode.com/submissions/detail/253276630/">1 ms</a>.
+     *
+     * @param x
+     * @param n
+     * @return
+     */
+    public static double myPow(double x, int n) {
+        double res = 1;
+        long absN = Math.abs((long) n);
+
+        while (absN > 0) {
+            if (absN % 2 == 1) res *= x; // store whatever we have calculated so far in the final result
+            x *= x;
+            absN /= 2;
+        }
+        return n < 0 ? 1 / res : res;
+    }
+
+    public static void main(String[] args) {
+        assertEquals(1024.0, myPowNaive(2.0, 10));
+        assertEquals(0.25, myPowNaive(2.0, -2));
+        assertEquals(0.0, myPowNaive(0.00001, 2147483647));
+
+        assertEquals(1024.0, myPow(2.0, 10));
+        assertEquals(0.25, myPow(2.0, -2));
+        assertEquals(0.0, myPow(0.00001, 2147483647));
+    }
+}

src/main/java/com/leetcode/strings/AnagramsInString.java

@@ -55,7 +55,7 @@ private static List<Integer> findAllAnagramsInTextNaive(String text, String patt
      * where,
      * n = length of text or number of characters in text
      * <p>
-     * Runtime: <a href="https://leetcode.com/submissions/detail/222911434/">7 ms on leetcode</a>.
+     * Runtime: <a href="https://leetcode.com/submissions/detail/253261320/">6 ms</a>.
      *
      * @param text
      * @param pattern