题解 | #24点运算#

let str;
let flag;
let text = "";
const d = { 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9, 10: 10, J: 11, Q: 12, K: 13, A: 1, 2: 2 }
while ((str = readline())) {
  let arr = str.split(" ")
  flag = "NONE";
  if (!arr.includes("joker") && !arr.includes("JOKER")) {
    dfs(0, 0, arr, text);
  } else {
    flag = "ERROR";
  }

  print(flag === "DONE" ? text : flag);
}

function dfs(step, sum, arr, res) {
  if (step == 4) {
    if (sum == 24) {
      flag = "DONE";
      text = res
      return;
    }
  } else {
    step++;
    for (let index in arr) {
      let _arr = JSON.parse(JSON.stringify(arr));
      let num = _arr.splice(index, 1)[0];
      if(step == 1){
        dfs(step, sum + d[num], _arr, `${num}`);
      }else {
        dfs(step, sum + d[num], _arr, `${res}+${num}`);
        dfs(step, sum - d[num], _arr, `${res}-${num}`);
        dfs(step, sum * d[num], _arr, `${res}*${num}`);
        dfs(step, sum / d[num], _arr, `${res}/${num}`);        
      }

    }
  }
}