JS中for循环的常见题型

// 1-10000以内的完数
// 完数：因子之和相加等于这个数
// 例如：6的因子为1，2，3：1+2+3=6

let i ,j;
let sum ;
for(i=1;i<=10000;i++){
    sum = 0;
    for(j=1;j<i;j++){
        if(i%j == 0){
            sum +=j;
        }
    }
    if(i == sum){
            console.log(i)
    }
}

// 让用户输入行数，使用for循环嵌套打出正着的星星出来，行数等于用户输入的数字

let readline = require("readline-sync");
console.log("请输入行数");
let line = readline.question("");
let strSpace = "";
let strStar = "";
let str = "";
for(let i = 1;i<=line;i++){
    for(let j =1;j<=line-i;j++){
        strSpace = strSpace + " ";
    }
    for(let k = 1;k<=2*i-1;k++){
        strStar = strStar + "*";
    }
    str = strSpace + strStar;
    console.log(str);
    str = "";
    strSpace = "";
    strStar = "";
}

// 让用户输入行数，使用for循环嵌套打出倒着的星星出来，行数等于用户输入的数字

let readline = require("readline-sync");
console.log("请输入行数");
let line = readline.question("");
let strSpace = "";
let strStar = "";
let str = "";
for(let n =1;n<=line;n++){
    for(let i=1;i<=n-1;i++){
        strSpace=strSpace+" ";
    }
    for(let j=1;j<=line*2+1-2*n;j++){
        strStar=strStar+"*";
    }
    str=strSpace+strStar;
    console.log(str);
    str = "";
    strSpace = "";
    strStar = "";
}

// 有1，2，3，4这么4个数，能组成多少个互不相同且不含有重复数字的三位数？都是多少？  

let sum =0;
for(let a =1;a<=4;a++){
    for(let b = 1;b<=4;b++){
        if(a === b){
            continue;
        }
        for(let c =1;c<=4;c++){
            if(a === c || b === c){
                continue;
            }
            console.log(a,b,c);
            sum++;
        }
    }
}console.log(sum);

let arr = [[2,3,6,8],[5,7,0,9],[1,3,5,7] ];
let str = [];

for(let i = 0;i<arr[0].length;i++){
   str[i] = [];
}
console.log(str)
for(let j =0;j<arr.length;j++){
    for(let k =0;k<arr[j].length;k++){
        str[k][j]=arr[j][k];
    }
}
console.log(str);