Added task 307

Author: javadev

src/main/java/s0307.range.sum.query.mutable/NumArray.java

@@ -0,0 +1,40 @@
+package s0307.range.sum.query.mutable;
+
+public class NumArray {
+    private int[] nums;
+    private int sum;
+
+    public NumArray(int[] nums) {
+        this.nums = nums;
+        sum = 0;
+        for (int i = 0; i < nums.length; i++) {
+            sum += nums[i];
+        }
+    }
+
+    public void update(int index, int val) {
+        sum -= nums[index] - val;
+        nums[index] = val;
+    }
+
+    public int sumRange(int left, int right) {
+        int sumRange = 0;
+        if ((right - left) < nums.length / 2) {
+            // Array to sum is less than half
+            for (int i = left; i <= right; i++) {
+                sumRange += nums[i];
+            }
+        } else {
+            // Array to sum is more than half
+            // Better to take total sum and substract the numbers not in range
+            sumRange = sum;
+            for (int i = 0; i < left; i++) {
+                sumRange -= nums[i];
+            }
+            for (int i = right + 1; i < nums.length; i++) {
+                sumRange -= nums[i];
+            }
+        }
+        return sumRange;
+    }
+}

src/test/java/s0307.range.sum.query.mutable/NumArrayTest.java

@@ -0,0 +1,16 @@
+package s0307.range.sum.query.mutable;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.Test;
+
+public class NumArrayTest {
+    @Test
+    public void createSumUpdateSum() {
+        NumArray numArray = new NumArray(new int[] {1, 3, 5});
+        assertThat(numArray.sumRange(0, 2), equalTo(9));
+        numArray.update(1, 2);
+        assertThat(numArray.sumRange(0, 2), equalTo(8));
+    }
+}