// 12 ，3，4 兩個數字組合 最后結果 應該是// 13// 14// 23// 24// 34// 這5種 用程序 怎么算出來// 是求組合的算法// var arr = [12, 3, 4];// var len = arr.length;// var result = [];// for (var i = 0; i < len; i++) {// for (var j = i + 1; j < len; j++) {// for (var k = 0; k < String(arr[i]).length; k++) {// for (var m = 0; m < String(arr[j]).length; m++) {// result.push(Number(String(arr[i]).charAt(k)+String(arr[j]).charAt(m)));// }// }// }// }// console.log(result);var arr = [12, 3, 4];var len = arr.length;var result = [];var indexs = {};function combination(ind, start) {  start++;  if (start > 1) {    return;  }  if (!indexs[start]) {    indexs[start] = 0;  }  for (indexs[start] = ind; indexs[start] < len; indexs[start]++) {    combination(indexs[start] + 1, start);    if (start == 1) {      var one = String(arr[indexs[start - 1]]);      var two = String(arr[indexs[start]]);      for (var k = 0; k < one.length; k++) {        for (var m = 0; m < two.length; m++) {          result.push(Number(one.charAt(k) + two.charAt(m)));        }      }    }  }}combination(0, -1);console.log(result);