js实现算法

JavaScript 实现常见算法的方法

排序算法

快速排序的实现：

function quickSort(arr) {
  if (arr.length <= 1) return arr;
  const pivot = arr[0];
  const left = [];
  const right = [];
  for (let i = 1; i < arr.length; i++) {
    arr[i] < pivot ? left.push(arr[i]) : right.push(arr[i]);
  }
  return [...quickSort(left), pivot, ...quickSort(right)];
}

归并排序的实现：

function mergeSort(arr) {
  if (arr.length <= 1) return arr;
  const mid = Math.floor(arr.length / 2);
  const left = mergeSort(arr.slice(0, mid));
  const right = mergeSort(arr.slice(mid));
  return merge(left, right);
}

function merge(left, right) {
  let result = [];
  while (left.length && right.length) {
    left[0] < right[0] ? result.push(left.shift()) : result.push(right.shift());
  }
  return [...result, ...left, ...right];
}

搜索算法

二分查找的实现：

function binarySearch(arr, target) {
  let left = 0;
  let right = arr.length - 1;
  while (left <= right) {
    const mid = Math.floor((left + right) / 2);
    if (arr[mid] === target) return mid;
    arr[mid] < target ? left = mid + 1 : right = mid - 1;
  }
  return -1;
}

动态规划

斐波那契数列的优化实现：

function fibonacci(n, memo = {}) {
  if (n in memo) return memo[n];
  if (n <= 2) return 1;
  memo[n] = fibonacci(n - 1, memo) + fibonacci(n - 2, memo);
  return memo[n];
}

图算法

Dijkstra最短路径算法：

function dijkstra(graph, start) {
  const distances = {};
  const visited = new Set();
  const nodes = Object.keys(graph);

  nodes.forEach(node => distances[node] = Infinity);
  distances[start] = 0;

  while (nodes.length) {
    nodes.sort((a, b) => distances[a] - distances[b]);
    const closest = nodes.shift();

    if (distances[closest] === Infinity) break;
    visited.add(closest);

    Object.keys(graph[closest]).forEach(neighbor => {
      if (!visited.has(neighbor)) {
        const newDistance = distances[closest] + graph[closest][neighbor];
        distances[neighbor] = Math.min(distances[neighbor], newDistance);
      }
    });
  }
  return distances;
}

数据结构实现

链表的实现：

class ListNode {
  constructor(val) {
    this.val = val;
    this.next = null;
  }
}

class LinkedList {
  constructor() {
    this.head = null;
  }

  append(val) {
    const newNode = new ListNode(val);
    if (!this.head) {
      this.head = newNode;
      return;
    }
    let current = this.head;
    while (current.next) current = current.next;
    current.next = newNode;
  }
}

实用算法技巧

洗牌算法（Fisher-Yates）：

function shuffle(array) {
  for (let i = array.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [array[i], array[j]] = [array[j], array[i]];
  }
  return array;
}

这些实现涵盖了JavaScript中常见算法的基本应用，可以根据具体需求进行修改和优化。算法实现时需要注意边界条件和性能优化，特别是对于大规模数据处理的情况。