编码面试中解决问题的终极指南

/** * finds a pair of numbers in a sorted array that sum up to a target value. * uses the two-pointer technique for efficient searching. *  * @param {number[]} arr - the sorted array of numbers to search through. * @param {number} target - the target sum to find. * @returns {number[]|null} - returns an array containing the pair if found, or null if not found. */function findpairwithsum(arr, target) {  // initialize two pointers: one at the start and one at the end of the array  let left = 0;  let right = arr.length - 1;  // continue searching while the left pointer is less than the right pointer  while (left < right) {    console.log(`checking pair: ${arr[left]} and ${arr[right]}`);    // calculate the sum of the current pair    const sum = arr[left] + arr[right];    if (sum === target) {      // if the sum equals the target, we've found our pair      console.log(`found pair: ${arr[left]} + ${arr[right]} = ${target}`);      return [arr[left], arr[right]];    } else if (sum < target) {      // if the sum is less than the target, we need a larger sum      // so, we move the left pointer to the right to increase the sum      console.log(`sum ${sum} is less than target ${target}, moving left pointer`);      left++;    } else {      // if the sum is greater than the target, we need a smaller sum      // so, we move the right pointer to the left to decrease the sum      console.log(`sum ${sum} is greater than target ${target}, moving right pointer`);      right--;    }  }  // if we've exhausted all possibilities without finding a pair, return null  console.log("no pair found");  return null;}// example usageconst sortedarray = [1, 3, 5, 7, 9, 11];const targetsum = 14;findpairwithsum(sortedarray, targetsum);

/** * finds the maximum sum of a subarray of size k in the given array. * @param {number[]} arr - the input array of numbers. * @param {number} k - the size of the subarray. * @returns {number|null} the maximum sum of a subarray of size k, or null if the array length is less than k. */function maxsubarraysum(arr, k) {  // check if the array length is less than k  if (arr.length < k) {    console.log("array length is less than k");    return null;  }  let maxsum = 0;  let windowsum = 0;  // calculate sum of first window  for (let i = 0; i < k; i++) {    windowsum += arr[i];  }  maxsum = windowsum;  console.log(`initial window sum: ${windowsum}, window: [${arr.slice(0, k)}]`);  // slide the window and update the maximum sum  for (let i = k; i  maxsum) {      maxsum = windowsum;      console.log(`new max sum found: ${maxsum}, window: [${arr.slice(i - k + 1, i + 1)}]`);    }  }  console.log(`final max sum: ${maxsum}`);  return maxsum;}// example usageconst array = [1, 4, 2, 10, 23, 3, 1, 0, 20];const k = 4;maxsubarraysum(array, k);

/** * finds the first non-repeating character in a given string. * @param {string} str - the input string to search. * @returns {string|null} the first non-repeating character, or null if not found. */function firstnonrepeatingchar(str) {  const charcount = new map();  // count occurrences of each character  for (let char of str) {    charcount.set(char, (charcount.get(char) || 0) + 1);    console.log(`character ${char} count: ${charcount.get(char)}`);  }  // find the first character with count 1  for (let char of str) {    if (charcount.get(char) === 1) {      console.log(`first non-repeating character found: ${char}`);      return char;    }  }  console.log("no non-repeating character found");  return null;}// example usageconst inputstring = "aabccdeff";firstnonrepeatingchar(inputstring);

// create a new mapconst fruitinventory = new map();// set key-value pairsfruitinventory.set('apple', 5);fruitinventory.set('banana', 3);fruitinventory.set('orange', 2);console.log('initial inventory:', fruitinventory);// get a value using a keyconsole.log('number of apples:', fruitinventory.get('apple'));// check if a key existsconsole.log('do we have pears?', fruitinventory.has('pear'));// update a valuefruitinventory.set('banana', fruitinventory.get('banana') + 2);console.log('updated banana count:', fruitinventory.get('banana'));// delete a key-value pairfruitinventory.delete('orange');console.log('inventory after removing oranges:', fruitinventory);// iterate over the mapconsole.log('current inventory:');fruitinventory.foreach((count, fruit) => {  console.log(`${fruit}: ${count}`);});// get the size of the mapconsole.log('number of fruit types:', fruitinventory.size);// clear the entire mapfruitinventory.clear();console.log('inventory after clearing:', fruitinventory);

/** * calculates the nth fibonacci number using dynamic programming. * @param {number} n - the position of the fibonacci number to calculate. * @returns {number} the nth fibonacci number. */function fibonacci(n) {  // initialize an array to store fibonacci numbers  const fib = new array(n + 1);  // base cases  fib[0] = 0;  fib[1] = 1;  console.log(`f(0) = ${fib[0]}`);  console.log(`f(1) = ${fib[1]}`);  // calculate fibonacci numbers iteratively  for (let i = 2; i <= n; i++) {    fib[i] = fib[i - 1] + fib[i - 2];    console.log(`f(${i}) = ${fib[i]}`);  }  return fib[n];}// example usageconst n = 10;console.log(`the ${n}th fibonacci number is:`, fibonacci(n));

/** * performs a binary search on a sorted array. * @param {number[]} arr - the sorted array to search. * @param {number} target - the value to find. * @returns {number} the index of the target if found, or -1 if not found. */function binarysearch(arr, target) {  let left = 0;  let right = arr.length - 1;  while (left <= right) {    const mid = math.floor((left + right) / 2);    console.log(`searching in range [${left}, ${right}], mid = ${mid}`);    if (arr[mid] === target) {      console.log(`target ${target} found at index ${mid}`);      return mid;    } else if (arr[mid] < target) {      console.log(`${arr[mid]}  ${target}, searching left half`);      right = mid - 1;    }  }  console.log(`target ${target} not found in the array`);  return -1;}// example usageconst sortedarray = [1, 3, 5, 7, 9, 11, 13, 15];const target = 7;binarysearch(sortedarray, target);

class graph {  constructor() {    this.adjacencylist = {};  }  addvertex(vertex) {    if (!this.adjacencylist[vertex]) this.adjacencylist[vertex] = [];  }  addedge(v1, v2) {    this.adjacencylist[v1].push(v2);    this.adjacencylist[v2].push(v1);  }  dfs(start) {    const result = [];    const visited = {};    const adjacencylist = this.adjacencylist;    (function dfshelper(vertex) {      if (!vertex) return null;      visited[vertex] = true;      result.push(vertex);      console.log(`visiting vertex: ${vertex}`);      adjacencylist[vertex].foreach(neighbor => {        if (!visited[neighbor]) {          console.log(`exploring neighbor: ${neighbor} of vertex: ${vertex}`);          return dfshelper(neighbor);        } else {          console.log(`neighbor: ${neighbor} already visited`);        }      });    })(start);    return result;  }}// example usageconst graph = new graph();['a', 'b', 'c', 'd', 'e', 'f'].foreach(vertex => graph.addvertex(vertex));graph.addedge('a', 'b');graph.addedge('a', 'c');graph.addedge('b', 'd');graph.addedge('c', 'e');graph.addedge('d', 'e');graph.addedge('d', 'f');graph.addedge('e', 'f');console.log(graph.dfs('a'));

class graph {  // ... (same constructor, addvertex, and addedge methods as above)  bfs(start) {    const queue = [start];    const result = [];    const visited = {};    visited[start] = true;    while (queue.length) {      let vertex = queue.shift();      result.push(vertex);      console.log(`visiting vertex: ${vertex}`);      this.adjacencylist[vertex].foreach(neighbor => {        if (!visited[neighbor]) {          visited[neighbor] = true;          queue.push(neighbor);          console.log(`adding neighbor: ${neighbor} to queue`);        } else {          console.log(`neighbor: ${neighbor} already visited`);        }      });    }    return result;  }}// example usage (using the same graph as in dfs example)console.log(graph.bfs('a'));

class minheap {  constructor() {    this.heap = [];  }  getparentindex(i) {    return math.floor((i - 1) / 2);  }  getleftchildindex(i) {    return 2 * i + 1;  }  getrightchildindex(i) {    return 2 * i + 2;  }  swap(i1, i2) {    [this.heap[i1], this.heap[i2]] = [this.heap[i2], this.heap[i1]];  }  insert(key) {    this.heap.push(key);    this.heapifyup(this.heap.length - 1);  }  heapifyup(i) {    let currentindex = i;    while (this.heap[currentindex] < this.heap[this.getparentindex(currentindex)]) {      this.swap(currentindex, this.getparentindex(currentindex));      currentindex = this.getparentindex(currentindex);    }  }  extractmin() {    if (this.heap.length === 0) return null;    if (this.heap.length === 1) return this.heap.pop();    const min = this.heap[0];    this.heap[0] = this.heap.pop();    this.heapifydown(0);    return min;  }  heapifydown(i) {    let smallest = i;    const left = this.getleftchildindex(i);    const right = this.getrightchildindex(i);    if (left < this.heap.length && this.heap[left] < this.heap[smallest]) {      smallest = left;    }    if (right < this.heap.length && this.heap[right]  minheap.insert(num));console.log(minheap.heap);console.log(minheap.extractmin());console.log(minheap.heap);

class trienode {  constructor() {    this.children = {};    this.isendofword = false;  }}class trie {  constructor() {    this.root = new trienode();  }  insert(word) {    let current = this.root;    for (let char of word) {      if (!current.children[char]) {        current.children[char] = new trienode();      }      current = current.children[char];    }    current.isendofword = true;    console.log(`inserted word: ${word}`);  }  search(word) {    let current = this.root;    for (let char of word) {      if (!current.children[char]) {        console.log(`word ${word} not found`);        return false;      }      current = current.children[char];    }    console.log(`word ${word} ${current.isendofword ? 'found' : 'not found'}`);    return current.isendofword;  }  startswith(prefix) {    let current = this.root;    for (let char of prefix) {      if (!current.children[char]) {        console.log(`no words start with ${prefix}`);        return false;      }      current = current.children[char];    }    console.log(`found words starting with ${prefix}`);    return true;  }}// example usageconst trie = new trie();['apple', 'app', 'apricot', 'banana'].foreach(word => trie.insert(word));trie.search('app');trie.search('application');trie.startswith('app');trie.startswith('ban');

class unionfind {  constructor(size) {    this.parent = array(size).fill().map((_, i) => i);    this.rank = array(size).fill(0);    this.count = size;  }  find(x) {    if (this.parent[x] !== x) {      this.parent[x] = this.find(this.parent[x]);    }    return this.parent[x];  }  union(x, y) {    let rootx = this.find(x);    let rooty = this.find(y);    if (rootx === rooty) return;    if (this.rank[rootx] < this.rank[rooty]) {      [rootx, rooty] = [rooty, rootx];    }    this.parent[rooty] = rootx;    if (this.rank[rootx] === this.rank[rooty]) {      this.rank[rootx]++;    }    this.count--;    console.log(`united ${x} and ${y}`);  }  connected(x, y) {    return this.find(x) === this.find(y);  }}// example usageconst uf = new unionfind(10);uf.union(0, 1);uf.union(2, 3);uf.union(4, 5);uf.union(6, 7);uf.union(8, 9);uf.union(0, 2);uf.union(4, 6);uf.union(0, 4);console.log(uf.connected(1, 5)); // should print: trueconsole.log(uf.connected(7, 9)); // should print: false

class Graph {  constructor() {    this.adjacencyList = {};  }  addVertex(vertex) {    if (!this.adjacencyList[vertex]) this.adjacencyList[vertex] = [];  }  addEdge(v1, v2) {    this.adjacencyList[v1].push(v2);  }  topologicalSort() {    const visited = {};    const stack = [];    const dfsHelper = (vertex) => {      visited[vertex] = true;      this.adjacencyList[vertex].forEach(neighbor => {        if (!visited[neighbor]) {          dfsHelper(neighbor);        }      });      stack.push(vertex);      console.log(`Added ${vertex} to stack`);    };    for (let vertex in this.adjacencyList) {      if (!visited[vertex]) {        dfsHelper(vertex);      }    }    return stack.reverse();  }}// Example usageconst graph = new Graph();['A', 'B', 'C', 'D', 'E', 'F'].forEach(vertex => graph.addVertex(vertex));graph.addEdge('A', 'C');graph.addEdge('B', 'C');graph.addEdge('B', 'D');graph.addEdge('C', 'E');graph.addEdge('D', 'F');graph.addEdge('E', 'F');console.log(graph.topologicalSort());