add: SumBetweenRange

Author: Jer3myYu

java/Prefix Sums/SumBetweenRange.java

@@ -0,0 +1,18 @@
+public class SumBetweenRange {
+    int[] prefixSum;
+
+    public SumBetweenRange(int[] nums) {
+        this.prefixSum = new int[nums.length];
+        this.prefixSum[0] = nums[0];
+        for (int i = 1; i < nums.length; i++) {
+            this.prefixSum[i] = this.prefixSum[i - 1] + nums[i];
+        }
+    }
+
+    public int sumRange(int i, int j) {
+        if (i == 0) {
+            return this.prefixSum[j];
+        }
+        return this.prefixSum[j] - this.prefixSum[i - 1];
+    }
+}