[HAI] open lesson maxSum

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lib/maxSum/index.ts

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+import { maxSum } from "./maxSum";
+
+export default maxSum;

lib/maxSum/maxSum.test.ts

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+import { describe, it, expect } from "vitest";
+import { maxSum } from "./maxSum.ts";
+
+describe("maxSum", () => {
+
+  it("[3, 2, 5, 9, 4 ,1] k=3 answer 18", () => {
+    const NUMS = [3, 2, 5, 9, 4, 1];
+    expect(maxSum(NUMS, 3)).toBe(18);
+  });
+
+  it("[0, 1, 2, 8, 1 ,11, 10, 0, 0 ,5] k=4 answer 18", () => {
+    const NUMS = [0, 1, 2, 8, 1, 11, 10, 0, 0, 5];
+    expect(maxSum(NUMS, 4)).toBe(30);
+  });
+
+});

lib/maxSum/maxSum.ts

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+export function maxSum(nums: number[], k: number) {
+  const L = nums.length;
+
+  if (k > L) return 0;
+
+  /* считаем первое окно */
+  let sum = 0;
+  for (let i = 0; i < k; i++) {
+    sum += nums[i];
+  }
+  /* смещем окно, переситываем результат, выбираем максимальный */
+  let maxSumRes = sum;
+  for (let i = k; i < L; i++) {
+    sum = sum - nums[i - k] + nums[i];
+    maxSumRes = Math.max(maxSumRes, sum);
+  }
+
+
+  return maxSumRes;
+};