[casentino] WEEK 02 solutions

3sum/casentino.ts

@@ -0,0 +1,34 @@
+function threeSum(nums: number[]): number[][] {
+  const sortedNums = nums.sort((a, b) => a - b);
+  const results: number[][] = [];
+  for (let i = 0; i < sortedNums.length - 2; i++) {
+    const current = sortedNums[i];
+    if (current > 0) {
+      return results;
+    }
+    if (i > 0 && current === sortedNums[i - 1]) {
+      continue;
+    }
+    let left = i + 1;
+    let right = sortedNums.length - 1;
+    while (left < right) {
+      const sum = current + sortedNums[left] + sortedNums[right];
+      if (sum > 0) {
+        right -= 1;
+      } else if (sum < 0) {
+        left += 1;
+      } else {
+        results.push([current, sortedNums[left], sortedNums[right]]);
+        left += 1;
+        right -= 1;
+        while (left < right && sortedNums[left] === sortedNums[left - 1]) {
+          left += 1;
+        }
+        while (left < right && sortedNums[right] === sortedNums[right + 1]) {
+          right -= 1;
+        }
+      }
+    }
+  }
+  return results;
+}

climbing-stairs/casentino.ts

@@ -0,0 +1,17 @@
+function climbStairs(n: number): number {
+  const memo = new Array(n + 1).fill(-1);
+  function climb(stair: number) {
+    if (stair === 0) {
+      return 1;
+    }
+    if (stair < 0) {
+      return 0;
+    }
+    if (memo[stair] !== -1) {
+      return memo[stair];
+    }
+    memo[stair] = climb(stair - 1) + climb(stair - 2);
+    return memo[stair];
+  }
+  return climb(n);
+}

product-of-array-except-self/casentino.ts

@@ -0,0 +1,14 @@
+function productExceptSelf(nums: number[]): number[] {
+  const len = nums.length;
+  const result = new Array(len).fill(1);
+  let pre = 1;
+  let post = 1;
+  for (let i = 0; i < len; i++) {
+    result[i] *= pre;
+    pre *= nums[i];
+
+    result[len - i - 1] *= post;
+    post *= nums[len - i - 1];
+  }
+  return result;
+}

valid-anagram/casentino.ts

@@ -0,0 +1,16 @@
+function isAnagram(s: string, t: string): boolean {
+  if (s.length !== t.length) {
+    return false;
+  }
+  const count = new Array(26).fill(0);
+  for (let i = 0; i < s.length; i++) {
+    count[s.charCodeAt(i) - 97]++;
+    count[t.charCodeAt(i) - 97]--;
+  }
+  for (let c of count) {
+    if (c !== 0) {
+      return false;
+    }
+  }
+  return true;
+}

validate-binary-search-tree/casentino.ts

@@ -0,0 +1,39 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+class TreeNode {
+  val: number;
+  left: TreeNode | null;
+  right: TreeNode | null;
+  constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+    this.val = val === undefined ? 0 : val;
+    this.left = left === undefined ? null : left;
+    this.right = right === undefined ? null : right;
+  }
+}
+
+function isValidBST(root: TreeNode | null): boolean {
+  function recursiveSearch(node: TreeNode | null, min: number | null, max: number | null) {
+    if (!node) {
+      return true;
+    }
+    if (min !== null && node.val <= min) {
+      return false;
+    }
+    if (max !== null && node.val >= max) {
+      return false;
+    }
+    return recursiveSearch(node.left, min, node.val) && recursiveSearch(node.right, node.val, max);
+  }
+  return recursiveSearch(root, null, null);
+}