[Helena] Week 6 solutions

container-with-most-water/yolophg.js

@@ -0,0 +1,32 @@
+// Time Complexity: O(n)
+// Space Complexity: O(1)
+
+var maxArea = function(height) {
+    let left = 0;
+    let right = height.length - 1;
+
+    // to store the maximum area.
+    let maxArea = 0;
+
+    // iterate until the two pointers meet.
+    while (left < right) {
+        // calculate the width between the two pointers.
+        let width = right - left;
+
+        // calculate the area with the current area.
+        let currentArea = Math.min(height[left], height[right]) * width;
+
+        // update the maximum area if the current area is larger.
+        maxArea = Math.max(maxArea, currentArea);
+
+        // move the pointer to the shorter line towards the center.
+        if (height[left] < height[right]) {
+            left++;
+        } else {
+            right--;
+        }
+    }
+
+    // return the maximum area found.
+    return maxArea;
+};

find-minimum-in-rotated-sorted-array/yolophg.js

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+// Time Complexity: O(log n)
+// Space Complexity: O(1)
+
+var findMin = function(nums) {
+    // initialize left pointer.
+    let left = 0;
+    // initialize right pointer.
+    let right = nums.length - 1;
+
+    while (left < right) {
+        // calculate the middle index.
+        let mid = left + ((right - left) / 2 | 0);
+
+        // if the value at the middle index is bigger, move the left pointer to the right.
+        if (nums[mid] > nums[right]) {
+            left = mid + 1;
+        } else { // else, move the right pointer to the middle index.
+            right = mid;
+        }
+    }
+
+    // return the element which is the minimum pointed to by the left pointer.
+    return nums[left];
+};

longest-repeating-character-replacement/yolophg.js

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+// Time Complexity: O(n)
+// Space Complexity: O(1)
+
+var characterReplacement = function(s, k) {
+    let maxLen = 0; 
+    // initialize an array to store the count of each character.
+    let charCounts = new Array(26).fill(0); 
+    let start = 0;
+
+    // iterate the string with the end pointer.
+    for (let end = 0; end < s.length; end++) {
+        // calculate the index of the character.
+        let charIndex = s.charCodeAt(end) - 65; 
+        // update maxCount with the maximum count.
+        maxLen = Math.max(maxLen, ++charCounts[charIndex]); 
+
+        // move the start pointer and decrement the count at that position.
+        if (end - start + 1 - maxLen > k) {
+            charCounts[s.charCodeAt(start) - 65]--;
+            start++;
+        }
+    }
+
+    return s.length - start;
+};

longest-substring-without-repeating-characters/yolophg.js

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+// Time Complexity: O(n)
+// Space Complexity: O(n)
+
+var lengthOfLongestSubstring = function(s) {
+    let charSet = new Set();
+
+    let left = 0;
+    let right = 0;
+
+    let maxLength = 0;
+
+    // iterate the string.
+    while (right < s.length) {
+        if (!charSet.has(s[right])) {
+            // if the character isn't in the set, add it.
+            charSet.add(s[right]);
+            // move the right pointer to the right.
+            right++;
+            // update the maximum length if the current window is larger.
+            maxLength = Math.max(maxLength, right - left);
+        } else {
+            // if the character is in the set, remove the leftmost character.
+            charSet.delete(s[left]);
+            // move the left pointer to the right.
+            left++;
+        }
+    }
+
+    return maxLength;
+};

search-in-rotated-sorted-array/yolophg.js

@@ -0,0 +1,16 @@
+// Time Complexity: O(n)
+// Space Complexity: O(1)
+
+var search = function(nums, target) {
+    // iterate through each element.
+    for (let i = 0; i < nums.length; i++) {
+        // check if the current element is equal to the target.
+        if (nums[i] === target) {
+            // if found, return the index.
+            return i;
+        }
+    }
+
+    // if the loop completes without finding the target, return -1.
+    return -1;
+};