递归中的一元运算符前缀执行没有按预期工作

Question

我正在尝试计算给定组合范围和长度内的组合数量。下面是代码。

function generateCombination() {
const perm = [];
const permLength = 2;
const numberRange = 8;
let total = 0;
const getCombinations = (result, permLength, numberRange) => {
if (result.length === permLength) {
//console.log('result: ', result);
return 1;
}

for (var i = 0; i < numberRange; i++) {
if (result.indexOf(i) === -1) {
result.push(i);
total = total + getCombinations(result, permLength, numberRange);
result.pop();
}
}
return 0;
}

getCombinations(perm, permLength, numberRange);
console.log("total: ", total); // expected value "total:  56"
}
generateCombination();

CCD_ 1变量的控制台日志总是打印0。但下面的代码如预期的那样工作，CCD_ 2循环代码几乎没有变化。我不明白前缀在这里是如何工作的(somex=somex+fn(((。有人能帮忙吗？

// working solution
function generateCombination() {
const perm = [];
const permLength = 2;
const numberRange = 8;
let total = 0;
const getCombinations = (result, permLength, numberRange) => {
if (result.length === permLength) {
//console.log('result: ', result);
return 1;
}

for (var i = 0; i < numberRange; i++) {
if (result.indexOf(i) === -1) {
result.push(i);
if (getCombinations(result, permLength, numberRange)) {
total += 1;
}
result.pop();
}
}
return 0;
}

getCombinations(perm, permLength, numberRange);
console.log("total: ", total); // expected value is "total: 56" and working here
}
generateCombination();

我的问题是，我不明白，为什么解决方案1(顶部的解决方案(没有按预期工作(将total打印为0而不是56(？

感谢

Answer 1

您可以将total移动到getCombinations中，并在退出时返回此值。

function generateCombination() {
const perm = [];
const permLength = 2;
const numberRange = 8;
const getCombinations = (result, permLength, numberRange) => {
if (result.length === permLength) return 1;
let total = 0;

for (let i = 0; i < numberRange; i++) {
if (result.indexOf(i) === -1) {
result.push(i);
total += getCombinations(result, permLength, numberRange);
result.pop();
}
}
return total;
}

console.log("total: ", getCombinations(perm, permLength, numberRange)); // expected value "total:  56"
}
generateCombination();