Different Ways to Add Parentheses LeetCode solution in JavaScript

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var diffWaysToCompute = function (expression) {
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  //     We can iterate through the expression character-by-character.
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  // we can break the expression into two halves whenever we get an operator (+, -, *).
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  // The two parts can be calculated by recursively calling the function.
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  // Once we have the evaluation results from the left and right halves, we can combine them to produce all results.
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  return diffWaysRec({}, expression);
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};
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function diffWaysRec(map, expression) {
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  if (expression in map) {
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    return map[expression];
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  }
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  let result = [];
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  if (
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    !expression.includes("+") &&
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    !expression.includes("-") &&
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    !expression.includes("*")
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  ) {
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    result.push(parseInt(expression));
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  } else {
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    for (let i = 0; i < expression.length; i++) {
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      let char = expression[i];
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      if (isNaN(parseInt(char, 10))) {
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        //not a number , must it expression
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        //calculate lest and right now
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        let leftParts = diffWaysRec(map, expression.substring(0, i));
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        let rightParts = diffWaysRec(map, expression.substring(i + 1));
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        for (let l = 0; l < leftParts.length; l++) {
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          for (let r = 0; r < rightParts.length; r++) {
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            let left = leftParts[l];
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            let right = rightParts[r];
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            if (char === "+") {
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              result.push(parseInt(left) + parseInt(right));
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            }
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            if (char === "-") {
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              result.push(parseInt(left) - parseInt(right));
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            }
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            if (char === "*") {
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              result.push(parseInt(left) * parseInt(right));
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            }
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          }
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        }
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      }
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    }
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  }
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  map[expression] = result;
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  return result;
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}