算法的js实现

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算法的实现：

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;
    if (visited.has(closest)) continue;
    visited.add(closest);

    Object.keys(graph[closest]).forEach(neighbor => {
      const newDistance = distances[closest] + graph[closest][neighbor];
      if (newDistance < distances[neighbor]) {
        distances[neighbor] = newDistance;
      }
    });
  }
  return distances;
}

字符串算法

KMP字符串匹配的实现：

function kmpSearch(text, pattern) {
  const lps = computeLPSArray(pattern);
  let i = 0, j = 0;
  const result = [];

  while (i < text.length) {
    if (pattern[j] === text[i]) {
      i++;
      j++;
    }
    if (j === pattern.length) {
      result.push(i - j);
      j = lps[j - 1];
    } else if (i < text.length && pattern[j] !== text[i]) {
      j ? j = lps[j - 1] : i++;
    }
  }
  return result;
}

function computeLPSArray(pattern) {
  const lps = new Array(pattern.length).fill(0);
  let len = 0, i = 1;

  while (i < pattern.length) {
    if (pattern[i] === pattern[len]) {
      len++;
      lps[i] = len;
      i++;
    } else {
      len ? len = lps[len - 1] : lps[i++] = 0;
    }
  }
  return lps;
}

这些实现提供了常见算法在JavaScript中的基础版本，可以根据具体需求进行优化和扩展。实际应用中需要考虑输入数据的规模和边界条件处理。