LeetCode 两数之和算法题解 All In One

js / ts 实现两数之和

1. Two Sum

https://leetcode.com/problems/two-sum/description/

// 1. 双重循环 ✅
function twoSum(nums: number[], target: number): number[] {
  let temp;
  for (let i = 0; i < nums.length; i++){
    temp = nums[i]
    for (let j = i + 1; j < nums.length; j++){
      if (temp + nums[j] === target){
        return [i, j].sort()
      }
    }
  }
}

// 2. 对象字典 ✅ 
// function twoSum(nums: number[], target: number): number[] {
//   const dict = {}
//   for (const [i, item] of Object.entries(nums)) {
//     const temp = target - item;
//     if(dict[temp]) {
//       return [i, dict[temp]].sort()
//     } else {
//       dict[item] = i;
//     }
//   }
// };

// 3. Map 字典 ✅ 
// function twoSum(nums: number[], target: number): number[] {
//   const dict = new Map()
//   for (const [i, item] of Object.entries(nums)) {
//     const temp = target - item;
//     if(dict.has(temp)) {
//       return [i, dict.get(temp)].sort()
//     } else {
//       dict.set(item, i)
//     }
//   }
// };

// 3. hack 一次替换 ✅ 
// function twoSum(nums: number[], target: number): number[] {
//   for (const [i, item] of Object.entries(nums)) {
//     const temp = target - item;
//     const arr = [...nums]
//     // X 替换
//     arr[i] = `X`;
//     const index = arr.indexOf(temp)
//     if(index !== -1)  {
//       return [parseInt(i), index].sort()
//     }
//   }
// };

/* 

Testcase Source

[2,7,11,15]
9
[3,2,4]
6
[3,3]
6
[2,5,5,11]
10
[-1,-2,-3,-4,-5]
-8

 */

两数之和原理图解

HashMap / Map 字典

// 2.  HashMap 解法 O(n)
function twoSum(nums: number[], target: number): number[] {
  const map = new Map();
  let result:number[] = [];
  for(let i = 0; i < nums.length; i++) {
    let rest = target - nums[i];
    // 7 = 9 - 2
    // 2 = 9 - 7
    if(map.has(rest)) {
      result = [i, map.get(rest)];
      break;
    } else {
      map.set(nums[i], i);
    }
  }
  // console.log(`map`, [...map])
  // console.log(`result`, result)
  return result.sort((a, b) => a - b > 0 ? 1 : -1);
};

1. Two Sum

"use strict";

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2022-08-17
 * @modified
 *
 * @description 1. Two Sum
 * @description 1. 两数之和
 * @difficulty Easy
 * @ime_complexity O(n)
 * @space_complexity O(n)
 * @augments
 * @example
 * @link https://leetcode.com/problems/two-sum/
 * @link https://leetcode.cn/problems/two-sum/
 * @solutions
 *
 * @best_solutions
 *
 */

export {};

const log = console.log;

// 1. 暴力解法 O(n^2)
function twoSum(nums: number[], target: number): number[] {
  let result:number[] = [];
  for(let i = 0; i < nums.length; i++) {
    for(let j = i + 1; j < nums.length; j++) {
      if(nums[i] + nums[j] === target) {
        result = [i, j];
        break;
      }
    }
  }
  return result;
};


// 2. HashMap 解法 O(n)
function twoSum(nums: number[], target: number): number[] {
  const map = new Map();
  let result:number[] = [];
  for(let i = 0; i < nums.length; i++) {
    let rest = target - nums[i];
    // 7 = 9 - 2
    // 2 = 9 - 7
    if(map.has(rest)) {
      result = [i, map.get(rest)];
      break;
    } else {
      map.set(nums[i], i);
    }
  }
  // console.log(`map`, [...map])
  // console.log(`result`, result)
  return result.sort((a, b) => a - b > 0 ? 1 : -1);
};


type TestCasesO = {
  inputs: [number[], number];
  result: number[];
  desc: string;
}

// interface TestCasesI extends Array<any>{
//   [index: number]: TestCasesO;
// }

interface TestCasesI extends Array<TestCasesO>{
  // [index: number]: TestCasesO;
}

// 测试用例 test cases
const testCases: TestCasesI = [
  {
    inputs: [[2,7,11,15], 9],
    result: [0,1],
    desc: 'value equal to [0,1]',
  },
  {
    inputs: [[3,2,4], 6],
    result: [1,2],
    desc: 'value equal to [1,2]',
  },
  {
    inputs: [[3,3], 6],
    result: [0,1],
    desc: 'value equal to [0,1]',
  },
];

for (const [i, testCase] of testCases.entries()) {
  const [first, second] = testCase.inputs;
  const result = twoSum(first, second);
  log(`test case i result: \n`, result.join('') === testCase.result.join('') ? `passed ✅` : `failed ❌`, result);
  // log(`test case i =`, testCase);
}

// npx ts-node ./001\ two-sum.ts

https://leetcode.com/problems/two-sum/
https://leetcode.cn/problems/two-sum/