[hyer0705] WEEK 09 solutions

linked-list-cycle/hyer0705.ts

@@ -0,0 +1,25 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function hasCycle(head: ListNode | null): boolean {
+  if (!head || !head.next) return false;
+
+  let slow = head;
+  let fast = head;
+  while (fast && fast.next) {
+    slow = slow.next;
+    fast = fast.next.next;
+    if (slow === fast) return true;
+  }
+
+  return false;
+}

maximum-product-subarray/hyer0705.ts

@@ -0,0 +1,17 @@
+function maxProduct(nums: number[]): number {
+  let minValue = nums[0];
+  let maxValue = nums[0];
+  let result = nums[0];
+
+  for (let i = 1; i < nums.length; i++) {
+    const currentNum = nums[i];
+    [minValue, maxValue] = [
+      Math.min(currentNum, maxValue * currentNum, minValue * currentNum),
+      Math.max(currentNum, maxValue * currentNum, minValue * currentNum),
+    ];
+
+    result = Math.max(result, maxValue);
+  }
+
+  return result;
+}

minimum-window-substring/hyer0705.ts

@@ -0,0 +1,44 @@
+function minWindow(s: string, t: string): string {
+  const m = s.length;
+  const n = t.length;
+
+  if (m < n) return "";
+
+  let windowStart = 0;
+  let minLen = Infinity;
+  let substring = "";
+
+  let requiredChar = n;
+
+  const countCharMap = new Map<string, number>();
+  for (const ch of t) {
+    countCharMap.set(ch, (countCharMap.get(ch) || 0) + 1);
+  }
+
+  for (let windowEnd = 0; windowEnd < m; windowEnd++) {
+    const endChar = s[windowEnd];
+
+    if (countCharMap.has(endChar)) {
+      if (countCharMap.get(endChar)! > 0) requiredChar--;
+      countCharMap.set(endChar, (countCharMap.get(endChar) || 0) - 1);
+    }
+
+    while (requiredChar === 0) {
+      const currentLen = windowEnd - windowStart + 1;
+      if (currentLen < minLen) {
+        minLen = currentLen;
+        substring = s.substring(windowStart, windowEnd + 1);
+      }
+
+      const startChar = s[windowStart];
+      windowStart++;
+
+      if (countCharMap.has(startChar)) {
+        countCharMap.set(startChar, (countCharMap.get(startChar) || 0) + 1);
+        if (countCharMap.get(startChar)! > 0) requiredChar++;
+      }
+    }
+  }
+
+  return substring;
+}

pacific-atlantic-water-flow/hyer0705.ts

@@ -0,0 +1,54 @@
+function pacificAtlantic(heights: number[][]): number[][] {
+  const m = heights.length;
+  const n = heights[0].length;
+
+  const directions = [
+    [0, 1],
+    [0, -1],
+    [1, 0],
+    [-1, 0],
+  ];
+
+  const helper = (row: number, col: number): boolean[][] => {
+    const canReach: boolean[][] = Array.from({ length: m }, () => Array(n).fill(false));
+
+    const queue: [number, number][] = [];
+
+    for (let i = 0; i < n; i++) {
+      canReach[row][i] = true;
+      queue.push([row, i]);
+    }
+    for (let i = 0; i < m; i++) {
+      canReach[i][col] = true;
+      queue.push([i, col]);
+    }
+
+    while (queue.length > 0) {
+      const [cx, cy] = queue.shift()!;
+
+      for (const [dx, dy] of directions) {
+        const [nx, ny] = [cx + dx, cy + dy];
+
+        if (nx >= 0 && nx < m && ny >= 0 && ny < n && !canReach[nx][ny] && heights[cx][cy] <= heights[nx][ny]) {
+          canReach[nx][ny] = true;
+          queue.push([nx, ny]);
+        }
+      }
+    }
+
+    return canReach;
+  };
+
+  const canReachPacific: boolean[][] = helper(0, 0);
+  const canReachAtlantic: boolean[][] = helper(m - 1, n - 1);
+
+  const results: number[][] = [];
+
+  for (let i = 0; i < m; i++) {
+    for (let j = 0; j < n; j++) {
+      if (canReachPacific[i][j] && canReachAtlantic[i][j]) results.push([i, j]);
+    }
+  }
+
+  return results;
+}

sum-of-two-integers/hyer0705.ts

@@ -0,0 +1,10 @@
+function getSum(a: number, b: number): number {
+  while (b !== 0) {
+    let carry = (a & b) << 1;
+
+    a = a ^ b;
+
+    b = carry;
+  }
+  return a;
+}