leetcode

Author: ayoubzulfiqar

RangeSumQuery-Immutable/range_sum_query_immutable.go

@@ -1 +1,17 @@
 package main
+
+type NumArray struct {
+	sums []int
+}
+
+func Constructor(nums []int) NumArray {
+	sums := make([]int, len(nums)+1)
+	for i, v := range nums {
+		sums[i+1] += v + sums[i]
+	}
+	return NumArray{sums}
+}
+
+func (this *NumArray) SumRange(left int, right int) int {
+	return this.sums[right+1] - this.sums[left]
+}

RangeSumQuery-Immutable/range_sum_query_immutable.md

@@ -0,0 +1,81 @@
+# 🔥 Range Sum Query - Immutable 🔥 || 3 Solutions || Simple Fast and Easy || with Explanation
+
+## Solution - 1
+
+```dart
+class NumArray {
+  late List<int> prefixSum;
+
+  NumArray(List<int> nums) {
+    if (nums == 0) {
+      throw ArgumentError("Panic: Input is Empty");
+    }
+
+    this.prefixSum = List.filled(nums.length + 1, 0);
+
+    for (int i = 1; i <= nums.length; i++) {
+      prefixSum[i] = prefixSum[i - 1] + nums[i - 1];
+    }
+  }
+
+  int sumRange(int left, int right) {
+    if (left < 0 || right >= prefixSum.length - 1) {
+      throw RangeError("Panic: Input indices are out of bounds");
+    }
+
+    // Here both left and right are inclusive.
+    // right maps to right+1 in prefixSum. left maps to left+1 in prefixSum.
+    // To get the result subtract the prefixSum before left index from prefixSum at
+    // right index.
+    return prefixSum[right + 1] - prefixSum[left];
+  }
+}
+```
+
+## Solution - 2
+
+```dart
+class NumArray {
+  late List<int> nums;
+  late List<int> prefixSum;
+  NumArray(List<int> nums) {
+    this.nums = nums;
+    this.prefixSum = getPrefixSum();
+  }
+
+  int sumRange(int left, int right) {
+    if (left == 0) return prefixSum[right];
+    return prefixSum[right] - prefixSum[left - 1];
+  }
+
+  List<int> getPrefixSum() {
+    int sum = 0;
+    List<int> ans = List.filled(nums.length, 0);
+
+    for (int i = 0; i < nums.length; i++) {
+      sum += nums[i];
+      ans[i] = sum;
+    }
+
+    return ans;
+  }
+}
+```
+
+## Solution - 3
+
+```dart
+
+class NumArray {
+  List<int> arr = [];
+  NumArray(List<int> nums) {
+    this.arr = nums;
+  }
+
+  int sumRange(int left, int right) {
+    int sum = 0;
+    for (int i = left; i <= right; i++) sum += this.arr[i];
+    return sum;
+  }
+}
+```