Application of arrays in js and introduction to four methods of array deduplication (code)

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1. Input n, and output n rows of symmetrical arrays to form a pyramid:

function output(n) {
    for(let i=0;i<=n;i++){        
    let k=0;        
    var a=[];        
    for(let j=1;j<=2*i-1;j++){            
    if(j<=i){
               a.push(++k);
            }else{
               a.push(--k);
            } 
        }
        console.log(a)
    }
}

2. Array deduplication
Method 1: Traverse the array method

// 最简单数组去重法 
function unique1(array){ 
var n = []; //一个新的临时数组 
//遍历当前数组 
for(var i = 0; i < array.length; i++){ 
//如果当前数组的第i已经保存进了临时数组，那么跳过， 
//否则把当前项push到临时数组里面 
if (n.indexOf(array[i]) == -1) 
n.push(array[i]); 
} 
return n; 
}

Method Two: Array Subscript Judgment Method

function unique3(array){ var n = [array[0]]; //结果数组 
//从第二项开始遍历 
for(var i = 1; i < array.length; i++) { 
//如果当前数组的第i项在当前数组中第一次出现的位置不是i， 
//那么表示第i项是重复的，忽略掉。否则存入结果数组 
if (array.indexOf(array[i]) == i) 
n.push(array[i]); 
} 
return n; 
}

Method Three: Optimizing Traversing Array Method

// 思路：获取没重复的最右一值放入新数组 
function unique5(array){ 
var r = []; 
for(var i = 0, l = array.length; i < l; i++) { 
 for(var j = i + 1; j < l; j++) 
  if (array[i] === array[j]) 
  j = ++i; 
 r.push(array[i]); 
 } 
 return r; 
}

Method Four: Traversing Array

function unique(array){
    var a=[];    
    for(var i=0;i<array.length;i++){        
    var flag=0;        
    for(var j=0;j<a.length;j++){            
    if(array[i] == a[j])            
    var flag=1;
        }        
        if(flag==0){
           a.push(array[i]); 
        } 
    }    return a;
}

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