Completed Array-3 , 3 problems

h-index.ts

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+// Time complexity - O(nlog(n)), n number of citations
+// Space complexity - O(1)
+function hIndex(citations: number[]): number {
+	let result = 0;
+	citations.sort((a, b) => a - b);
+	let n = citations.length;
+	let l = 0;
+	let r = n - 1;
+
+	while (l <= r) {
+		const mid = Math.floor((l + r) / 2);
+
+		// possible h-index: number of papers from mid to n-1 (n - mid)
+		const diff = n - mid;
+
+		// if we found exact number of citations, return the h-index
+		if (citations[mid] === diff) return diff;
+
+		// citations at mid is higher than possible h-index
+		// to find a more possible citations count, search on the left side
+		if (citations[mid] > diff) {
+			r = mid - 1;
+		} else {
+			// citations at mid is lower than possible h-index
+			// to find a possible citations count, search on the right side
+			l = mid + 1;
+		}
+	}
+
+	// after the loop is complete, "l" points to the first index where citations[l] >= n - l.
+	return n - l;
+}
+
+// Time complexity - O(n), n number of citations
+// Space complexity - O(n + 1)
+
+// function hIndex(citations: number[]): number {
+// 	const n = citations.length;
+// 	const bucket = new Array(n + 1).fill(0);
+// 	for (let citation of citations) {
+// 		if (citation > n) {
+// 			bucket[n]++;
+// 		} else {
+// 			bucket[citation]++;
+// 		}
+// 	}
+// 	let sum = 0;
+// 	for (let i = n; i >= 0; i--) {
+// 		sum += bucket[i];
+
+// 		if (sum >= i) return i;
+// 	}
+// 	return -1;
+// }

rotate-array.ts

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+// Time complexity - O(n), n is the number of elements in nums array
+// Space complexity - O(1), no extra space used
+function rotate(nums: number[], k: number): void {
+	const n = nums.length;
+
+	// handling case if k is larger than n
+	k = k % n;
+
+	// reverse the entire array
+	reverse(0, n - 1);
+	// reverse the first k element
+	reverse(0, k - 1);
+	// reverse the k...n-1 element
+	reverse(k, n - 1);
+
+	function reverse(left: number, right: number) {
+		while (left < right) {
+			swap(left, right);
+			left++;
+			right--;
+		}
+	}
+
+	function swap(i: number, j: number) {
+		const temp = nums[i];
+		nums[i] = nums[j];
+		nums[j] = temp;
+	}
+}

trapping-rain-water.ts

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+function trap(height: number[]): number {
+	const n = height.length;
+	let r = n - 1;
+	let l = 0;
+	let lw = 0;
+	let rw = 0;
+	let result = 0;
+
+	while (l <= r) {
+		if (rw > lw) {
+			// rw acting as a dam, so we can trap water on the left side
+			if (height[l] > lw) {
+				lw = height[l];
+			} else {
+				result += 1 * lw - height[l];
+			}
+			l++;
+		} else {
+			// lw acting as a dam, so we can trap water on the right side
+			if (height[r] > rw) {
+				rw = height[r];
+			} else {
+				result += 1 * rw - height[r];
+			}
+			r--;
+		}
+	}
+	return result;
+}