两数之和

法一

• 哈希的思路

var twoSums = function (nums, target) {
  let hash = {}
  let ans = []
  for (let i = 0; i < nums.length; i++) {
    let temp = target - nums[i]
    if (hash[temp] !== undefined) {
      ans.push(hash[temp])
      ans.push(i)
      return ans
    } else {
      hash[nums[i]] = i
    }
  }
  return ans
}

let wk = [1, 2, 3, 4, 5, 6, 7, 8]
let target = 12
console.log(twoSums(wk, target))

• 打比方，找对象，主办方拿个本子，你需要什么样的对象，你一来就告诉主办⽅，然后看本子里有没有匹配的，有就直接牵手，没有就登记自己需要找的对象是什么标准

var twoSum = function (nums, target) {
  let obj = {};
  for (let i = 0; i < nums.length; i++) {
    let num = nums[i];
    let expect = target - num;
    if (num in obj) {
      // 找到了
      return [obj[num], i];
    } else {
      // 没找到，登记自己的需求
      obj[expect] = i;
      // console.log(obj)
    }
  }
};

• Map写法

var twoSum = function (nums, target) {
  // 构造哈希表
  var map = new Map();
  for (let i = 0; i < nums.length; i++) {
    let complement = target - nums[i];
    if (map.has(complement)) {
      return [map.get(complement), i];
    }
    map.set(nums[i], i);
  }
  console.log("No two sum solution");
};

法二

• 一个有趣的暴力方法

var twoSums = function (nums, target) {
  const len = nums.length
  while (true) {
    const i = parseInt(Math.random() * len)
    const j = parseInt(Math.random() * len)
    if (i !== j && nums[i] + nums[j] == target) {
      return [i, j]
    }
  }
}

let wk = [1, 2, 3, 4, 5, 6, 7, 8]
let target = 12
console.log(twoSums(wk, target))