常见的手写题

合并两个有序数组

var merge = function (nums1, m, nums2, n) {
  nums1.length = m;
  const nums = [];
  let p = 0;
  let q = 0;
  let maxL = Math.max(m, n);

  while (p < m && q < n) {
    if (nums1[p] < nums2[q]) {
      nums.push(nums1[p]);
      p++;
    } else {
      nums.push(nums2[q]);
      q++;
    }
  }

  while (p < m) {
    nums.push(nums1[p]);
    p++;
  }

  while (q < n) {
    nums.push(nums2[q]);
    q++;
  }

  return nums1 = nums;
};

最长回文字符串

const a = 'cbbd';
var longestPalindrome = function(s) {
  let res = ''; // 定义返回的最长回文子串
  for (let i = 0; i < s.length; i++) {
    match(i,i);
    match(i,i+1);
  }

  function match(m, n) {
    while( m >= 0 && n < s.length && s[m] === s[n]){
      m--;
      n++;
    }
    const t = s.slice(m+1,n);
    if (n-m-1 > res.length) {
      res = s.slice(m+1,n)
    }
  }

  return res;
};

const cc = longestPalindrome(a) 

检查死锁

const checkDeadLock = (dependencies) => {
  const graph = new Map();
  for ([from,to] of dependencies) {
    if (!graph.has(from)) {
      graph.set(from, new Set());
    }
    graph.get(from).add(to);
  }

  const visited = new Set();
  const recStack = new Set();

  const isCyclic = (node) => {
    if (resStack.has(node)) {      return true;    }    if (visited.has(node)) {      return false;    }
    visited.add(node);
    recStack.add(node);
    console.log('visited',visited)
    console.log('recStack',recStack)
    if(graph.has(node)){
      for (const neighbor of graph.get(node)) {
        if (!visited.has(neighbor)) {
          if (isCyclic(neighbor)) {
            return true;
          }
        }
      }
    }
    recStack.delete(node);
    return false;
  }

  for(const [node] of graph) {
    if(!visited.has(node)) {
      if(isCyclic(node)) {
        return true;
      }
    }
  }

  return false;
}

// 测试代码
const dependencies = [
  ['A', 'B'],
  ['A', 'C'],
  ['B', 'C'],
  ['B', 'D'],
  ['C', 'D'],
  ['D', 'A'],
];

console.log(checkDeadLock(dependencies)); 

查找公共时间范围

function getCommonSalePeriods(product1, product2) {
  let commonPeriods = [];

  for (let period1 of product1) {
    for (let period2 of product2) {
      let start1 = parseInt(period1[0], 10);
      let end1 = parseInt(period1[1], 10);
      let start2 = parseInt(period2[0], 10);
      let end2 = parseInt(period2[1], 10);

      let commonStart = Math.max(start1, start2);
      let commonEnd = Math.min(end1, end2);

      if (commonStart < commonEnd) {
        commonPeriods.push([commonStart.toString().padStart(4, '0'), commonEnd.toString().padStart(4, '0')]);
      }
    }
  }

  return commonPeriods;
}

let product1 = [['0720','0938'],['0812','0934']];
let product2 = [['0730','0830'],['0900','1000']];
console.log(getCommonSalePeriods(product1, product2));

防抖

function debounce(fn, delay) {
  let timer;
  return function() {
    const ctx = this;
    const args = arguments;
    if(timer) {
      clearTimeout(timer);
    }
    timer = setTimeout(() => {
      fn.apply(ctx, args);
    },delay);
  }
}

节流

function throttle(fn, delay) {
  let lastTime = 0;
  return function() {
    const ctx = this;
    const args = arguments;
    const newTime = Date.now();
    if(newTime - lastTime > delay) {
      fn.apply(ctx, args);
      lastTime = newTime;
    }
  }
}

手写Promise

class Promise {
  constructor(executor) {
    this.promStatus = 'pending';
    this.promResult = undefined;

    const resolve = (val) => {
      if (this.promStatus !== 'pending') {
        return;
      }
      this.promStatus = 'fulfilled';
      this.promResult = val;
    }

    const reject = (err) => {
      if (this.promStatus !== 'pending') {
        return;
      }
      this.promStatus = 'rejected';
      this.promResult = err;
    }

    const then = (onFulfilled, onRejected) => {
      return new Promise((resolve, reject) => {
        const handleCb = (cb) => {
          try {
            const res = cb(this.promResult);
            if (res instanceof Promise) {
              res.then((val) => resolve(val), err => reject(err))
            } else {
              resolve(res)
            }
          } catch (error) {
            reject(error)
          }
        }

        if (this.promStatus === 'fulfilled') {
          handleCb(onFulfilled);
        }
        if (this.promStatus === 'rejected') {
          handleCb(onRejected);
        }
      })
    }

    try {
      executor(resolve, reject);
    } catch(e) {
      reject(err);
    }
  }
}

深拷贝

function deepClone(obj) {
  if(typeof obj !== 'object') return obj;
  let newObj = obj.isArray() ? [] : {};
  for (prop in obj) {
    if(obj.hasOwnProperty(prop)) {
      newObj[prop] = typeof prop === 'object' ? deepClone(prop) : obj[prop];
    }
  }
  return newObj;
}