Different Ways to Add Parentheses

export function diffWaysToCompute(expression: string): number[] {
  function isOperator(char: string) {
    return /^[+\-*]$/.test(char);
  }
 
  function operate(x: number, y: number, operator: string) {
    if (operator === '+') {
      return x + y;
    }
    if (operator === '-') {
      return x - y;
    }
    return x * y;
  }
 
  function dfs(expression: string): number[] {
    const result: number[] = [];
    for (let i = 0; i < expression.length; i++) {
      if (isOperator(expression[i])) {
        const leftResult = dfs(expression.substring(0, i));
        const rightResult = dfs(expression.substring(i + 1));
        for (const x of leftResult) {
          for (const y of rightResult) {
            result.push(operate(x, y, expression[i]));
          }
        }
      }
    }
    if (result.length === 0) {
      result.push(parseInt(expression));
    }
    return result;
  }
 
  return dfs(expression);
}