Merge pull request #200 from yolophg/week13

[Helena] Week 13 solutions

Author: yolophg

insert-interval/yolophg.js

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+// Time Complexity: O(n log n)
+// Space Complexity: O(n)
+
+var insert = function (intervals, newInterval) {
+  // append the newInterval to the intervals array
+  intervals.push(newInterval);
+
+  // sort the intervals array by start time
+  intervals.sort((a, b) => a[0] - b[0]);
+
+  // to store merged intervals
+  let result = [];
+
+  // iterate through the sorted intervals array
+  for (let i = 0; i < intervals.length; i++) {
+    // if the result array is empty or the current interval does not overlap with the last interval
+    if (result.length === 0 || result[result.length - 1][1] < intervals[i][0]) {
+      result.push(intervals[i]); // Add the current interval to the result array
+    } else {
+      // if there is an overlap, merge the current interval with the last interval
+      result[result.length - 1][1] = Math.max(
+        result[result.length - 1][1],
+        intervals[i][1]
+      );
+    }
+  }
+
+  // return the final merged intervals
+  return result;
+};

meeting-rooms-ii/yolophg.js

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+// Time Complexity: O(n log n)
+// Space Complexity: O(n)
+
+export class Solution {
+  minMeetingRooms(intervals) {
+    // separate start and end times into different arrays
+    let startTimes = intervals.map((interval) => interval[0]);
+    let endTimes = intervals.map((interval) => interval[1]);
+
+    // sort the start and end times
+    startTimes.sort((a, b) => a - b);
+    endTimes.sort((a, b) => a - b);
+
+    let startPointer = 0;
+    let endPointer = 0;
+    let rooms = 0;
+    let maxRooms = 0;
+
+    // iterate over all the start times
+    while (startPointer < intervals.length) {
+      // if the start time is less than the end time, a new room is needed
+      if (startTimes[startPointer] < endTimes[endPointer]) {
+        rooms++;
+        startPointer++;
+      } else {
+        // if the start time is not less than the end time, free up a room
+        rooms--;
+        endPointer++;
+      }
+
+      // update the maximum number of rooms needed
+      maxRooms = Math.max(maxRooms, rooms);
+    }
+
+    // return the maximum number of rooms needed
+    return maxRooms;
+  }
+}

merge-intervals/yolophg.js

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+// Time Complexity: O(n log n)
+// Space Complexity: O(n)
+
+var merge = function (intervals) {
+  // sort the intervals by their start time
+  intervals.sort((a, b) => a[0] - b[0]);
+
+  // to manage merged intervals
+  let stack = [];
+
+  // push the first interval onto the stack
+  stack.push(intervals[0]);
+
+  // iterate through the sorted intervals
+  for (let i = 1; i < intervals.length; i++) {
+    // get the top interval from the stack
+    let top = stack[stack.length - 1];
+
+    // if the current interval overlaps with the top interval
+    if (top[1] >= intervals[i][0]) {
+      // merge the intervals by updating the end of the top interval
+      top[1] = Math.max(top[1], intervals[i][1]);
+    } else {
+      // if there is no overlap, push the current interval onto the stack
+      stack.push(intervals[i]);
+    }
+  }
+
+  // return the final merged intervals
+  return stack;
+};

non-overlapping-intervals/yolophg.js

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+// Time Complexity: O(n log n)
+// Space Complexity: O(1)
+
+var eraseOverlapIntervals = function (intervals) {
+  // sort the intervals based on their end times
+  intervals.sort((a, b) => a[1] - b[1]);
+
+  let end = intervals[0][1];
+  let count = 0;
+
+  // iterate through the sorted intervals
+  for (let i = 1; i < intervals.length; i++) {
+    if (intervals[i][0] < end) {
+      // overlapping interval found, increment the count
+      count++;
+    } else {
+      // no overlap, update the end to the current interval's end
+      end = intervals[i][1];
+    }
+  }
+
+  return count;
+};

rotate-image/yolophg.js

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+// Time Complexity: O(n^2)
+// Space Complexity: O(1)
+
+var rotate = function (matrix) {
+  const n = matrix.length;
+
+  // perform the rotation layer by layer
+  for (let layer = 0; layer < Math.floor(n / 2); layer++) {
+    let first = layer;
+    let last = n - 1 - layer;
+
+    for (let i = first; i < last; i++) {
+      let offset = i - first;
+
+      // save the top element
+      let top = matrix[first][i];
+
+      // move left element to top
+      matrix[first][i] = matrix[last - offset][first];
+
+      // move bottom element to left
+      matrix[last - offset][first] = matrix[last][last - offset];
+
+      // move right element to bottom
+      matrix[last][last - offset] = matrix[i][last];
+
+      // assign saved top element to right
+      matrix[i][last] = top;
+    }
+  }
+};