JS sum of two numbers

Sum of two numbers

Two layers of for loop

// O(n^2)
const twoNum = function(nums,target){
    
  for(let i =0;i<nums.length;i++){
    
    for(let j=i+1 ;j<nums.length;j++){
    
      if(nums[i]+nums[j]===target){
    
        return[i,j]
      }
    }
  }
}

Double pointer

//  When the array is ordered O(n)
const twoNum2 = function(nums,target){
    
  let i = 0 //  head 
  let j = nums.length-1 //  tail 
  while (i<j){
    
    const sum = nums[i]+nums[j]
    if(sum>target){
    
      j--
    }else if(sum<target){
    
      i++
    }else{
    
      return [i,j]
    }
  }
}

js Of map and set

Map

Is the structure of a set of key value pairs , With extremely fast search speed .

var m = new Map([['Michael', 95], ['Bob', 75], ['Tracy', 85]]);
m.get('Michael'); // 95

initialization Map We need a two-dimensional array , Or initialize a null directly Map.Map There are the following methods ：

var m = new Map(); //  empty Map
m.set('Adam', 67); //  Add new key-value
m.has('Adam'); //  Whether there is key 'Adam': true
m.get('Adam'); // 67
m.delete('Adam'); //  Delete key 'Adam'
m.get('Adam'); // undefined

• clear Remove all elements from the map .
• delete Remove the specified element from the map .
• forEach Perform the specified operation on each element in the map .
• get Returns the specified element in the map .
• has If the map contains the specified element , Then return to true.
• set Add a new element to the map .
• toString Returns the string representation of the mapping .
• valueOf Returns the original value of the specified object .

Set

Set It's a data structure called a set , It's also a group. key Set , But no storage. value. because key Can't repeat , therefore , stay Set in , No repeat key.

To create a Set, Need to provide a Array As input , Or create an empty Set

var s1 = new Set(); //  empty Set
var s2 = new Set([1, 2, 3]); //  contain 1, 2, 3

Set Properties of ：

• size： Returns the number of elements contained in the collection

Set Methods ：

Operation method

• add(value)： Add a new item to the collection
• delete(value)： Remove a value from the collection
• has(value)： If the value exists in the collection , return true, otherwise false
• clear(): Remove all items in the collection

Traversal methods

• keys()： Returns an array containing all the keys in the collection
• values()： Returns an array containing all the values in the collection
• entries： Returns an array containing all key value pairs in the collection
• forEach()： Used to perform some kind of operation on a collection member , no return value