Question

我为此标准的日常作业问题编写了解决方案，以递归方式解决Pascal的Triangle。 Console.log显示我的函数得出的答案。打印到div的innerHTML会将答案写入屏幕。逐步浏览chrome中的javascript调试器会显示解决方案数组在返回returnArray之前就存在。但是仍然在一天结束时，该函数返回“ undefined”。我不明白。

var generate = function (numRows) {
    var startRow = 1;
    var startCol = 1;
    var endRow = parseInt(numRows);
    var rowArray = [];
    var returnArray = [];
    var triVal;

    var triangle = function (row, col) {
        //base case
        if (col == 1 || col == row) {   //If the element is the either first or last element then initialize it with 1
            if (col == 1) {
                rowArray = [];
            }
            triVal = 1;
            rowArray.push(triVal);

            if (col == row) {
                returnArray.push(rowArray);
            }
        }
        else {
            //calc
            triVal = returnArray[row - 2][col - 2] + returnArray[row - 2][col - 1]
            triVal = typeof (triVal) === "undefined" ? 1 : triVal;
            rowArray.push(triVal);
        }
        if (col == row && row == endRow) { //stop the function and return                    
            console.log(JSON.stringify(returnArray));
            myDiv2.innerHTML = JSON.stringify(returnArray);
            return returnArray;                                
        }
        else {
            if (col == row) {
                col = 1;
                row = row + 1;
            } else {
                col = col + 1;
            }
            triangle(row, col);
        }
    }
    triangle(startRow, startCol);           
};  
var test = generate(4);
console.log('test is: ' + test); //Why does it returned undefined

我的第一个解决方案是使用形式函数generate（numRows）{};但作业要求解决方案采用表达式形式var generate = function（numRows）{};第一种方法返回我的预期结果。第二个没有。我不了解javascript的什么基础？

Answer 1

var generate = function (numRows) {

    //numRows == 0 ? numRows = 1 : numRows = numRows;
    if (numRows == 0) { return [];}

    var startRow = 1;
    var startCol = 1;
    var endRow = parseInt(numRows);
    var rowArray = [];
    var returnArray = [];
    var triVal;


    var triangle = function (row, col) {
        //base case
        if (col == 1 || col == row) {   //If the element is the either first or last element then initialize it with 1
            if (col == 1) {
                rowArray = [];
            }
            triVal = 1;
            rowArray.push(triVal);

            if (col == row) {
                returnArray.push(rowArray);
            }
        }
        else {
            //calc
            triVal = returnArray[row - 2][col - 2] + returnArray[row - 2][col - 1]
            triVal = typeof (triVal) === "undefined" ? 1 : triVal;
            rowArray.push(triVal);
        }
        if (col == row && row == endRow) { //stop the function and return                    
            console.log(JSON.stringify(returnArray));
            myDiv2.innerHTML = JSON.stringify(returnArray);
            return returnArray;                                
        }
        else {
            if (col == row) {
                col = 1;
                row = row + 1;
            } else {
                col = col + 1;
            }
            triangle(row, col);
        }
    }
    triangle(startRow, startCol);
    return returnArray;  //duh...the obvious answer!!! 
};  
var test = generate(1);
console.log('test is: ' + (JSON.stringify(test)));

为什么此递归javascript函数表达式返回undefined？

1 个答案: