Add Sum Between Range

Author: marttp

kotlin/Prefix Sums/SumBetweenRange.kt

@@ -0,0 +1,18 @@
+class SumBetweenRange(nums: IntArray) {
+
+    private val prefixSum: IntArray = IntArray(nums.size)
+
+    init {
+        prefixSum[0] = nums[0]
+        for (i in 1 until nums.size) {
+            prefixSum[i] = prefixSum[i - 1] + nums[i]
+        }
+    }
+
+    fun sumRange(i: Int, j: Int): Int {
+        if (i == 0) {
+            prefixSum[j]
+        }
+        return prefixSum[j] - prefixSum[i - 1]
+    }
+}