您正在通过递归进行所谓的深度优先搜索。每个人对递归的理解都略有不同。有些东西最终会让你点击。
我想在您的代码中添加一些注释，以帮助它打印出更自然的所发生情况的记录。希望这会有所帮助。
但我认为最重要的是通过缩进可视化递归的深度。当您在递归深度优先搜索期间记录时，您基本上是在制作一棵二叉树，其输出如下：
Root
Root > Left
Root > Right
它开始像这样递归嵌套：
Root
Root > Left
Root > Left > Left
Root > Left > Right
Root > Right
Root > Right > Left
Root > Right > Right
您正在创建“+5”和“*3”探索分支，而不是“左”和“右”路径。在您的递归中，您首先探索树的 +5 分支以寻找解决方案。如果你没有找到它，那么你探索树的 *3 分支。当什么都没有找到时，这只是意味着答案不在您正在考虑的分支上，必须在树的早期做出不同的选择。
当两种途径都尝试过但都没有成功时，似乎会发生一些回溯。但实际上，这只是一个假设的结论，我们说“如果我们+5，我们能到达那里吗？”或“如果我们 *3 我们能到达那里吗？”如果两者的答案都是否定的，那么你就无法从你所在的地方到达那里。您不必实际回溯，递归的美妙之处在于您在搜索中找到了您所在的位置，因为有人将您作为“如果...”的一部分调用。如果您的整个搜索结果都是空的，那没问题。您只需放弃当前的搜索分支，调用您的“某人”将在不同的分支上尝试其他内容。
您的递归状态（您正在探索的分支）保存在您的调用堆栈中。这就是我们真正“备份”的地方。
history 永远不会被修改。我们只是探索通过递归构造的不同版本的history。每个history 都是它自己的副本，它只会变得更长（搜索树中的左或右分支）或被放弃，并且在递归的其他地方从其他history 继续搜索。
所以这是您的代码，其中包含一些缩进和一些冗长的描述，希望能更紧密地与递归相关联。
function spaces(indent) {
return ' '.repeat(indent);
}
function findSolution(target) {
function nope(indent, history) {
console.log(spaces(indent) + `Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to ${target}, but not by starting from ${history}.`);
return false;
}
function badnews(history) {
console.log(`I've tried everything and there's just no way of getting to ${target}. :(`);
return false;
}
function find(current, which, history, indent) {
if (current == target) {
console.log(spaces(indent) + `${which}, and guess what...we finally found a solution! Because ${history} = ${current}. So we can stop now. :)`);
return history;
} else if (current > target) {
//console.log(`CURRENT AT NULL: ` + current);
console.log(spaces(indent) + `${which}, we reached a dead end because ${history} = ${current} which is unfortunately already bigger than ${target}.`);
return null;
} else {
console.log(spaces(indent) + `${which}, ${history} looks promising because it equals ${current}, which is still less than ${target}. We'll try two ways of getting to ${target} from here.`);
return find(current + 5, 'First, by adding 5', `(${history} + 5)`, indent+1) ||
find(current * 3, 'Second, by multiplying by 3', `(${history} * 3)`, indent+1) ||
nope(indent+1, history);
}
}
return find(1, 'Initially', "1", 0) || badnews();
}
console.log(`${findSolution(24)}`);
输出复制如下，以防万一。抱歉，没有包装输出，因为缩进更重要，因此您可以查看递归的深度，以及导致回溯的原因。如果您发现 sn-p 控制台输出更具可读性，则可以运行 sn-p。
Initially, 1 looks promising because it equals 1, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, (1 + 5) looks promising because it equals 6, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, ((1 + 5) + 5) looks promising because it equals 11, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, (((1 + 5) + 5) + 5) looks promising because it equals 16, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, ((((1 + 5) + 5) + 5) + 5) looks promising because it equals 21, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, we reached a dead end because (((((1 + 5) + 5) + 5) + 5) + 5) = 26 which is unfortunately already bigger than 24.
Second, by multiplying by 3, we reached a dead end because (((((1 + 5) + 5) + 5) + 5) * 3) = 63 which is unfortunately already bigger than 24.
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from ((((1 + 5) + 5) + 5) + 5).
Second, by multiplying by 3, we reached a dead end because ((((1 + 5) + 5) + 5) * 3) = 48 which is unfortunately already bigger than 24.
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from (((1 + 5) + 5) + 5).
Second, by multiplying by 3, we reached a dead end because (((1 + 5) + 5) * 3) = 33 which is unfortunately already bigger than 24.
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from ((1 + 5) + 5).
Second, by multiplying by 3, ((1 + 5) * 3) looks promising because it equals 18, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, (((1 + 5) * 3) + 5) looks promising because it equals 23, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, we reached a dead end because ((((1 + 5) * 3) + 5) + 5) = 28 which is unfortunately already bigger than 24.
Second, by multiplying by 3, we reached a dead end because ((((1 + 5) * 3) + 5) * 3) = 69 which is unfortunately already bigger than 24.
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from (((1 + 5) * 3) + 5).
Second, by multiplying by 3, we reached a dead end because (((1 + 5) * 3) * 3) = 54 which is unfortunately already bigger than 24.
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from ((1 + 5) * 3).
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from (1 + 5).
Second, by multiplying by 3, (1 * 3) looks promising because it equals 3, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, ((1 * 3) + 5) looks promising because it equals 8, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, (((1 * 3) + 5) + 5) looks promising because it equals 13, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, ((((1 * 3) + 5) + 5) + 5) looks promising because it equals 18, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, (((((1 * 3) + 5) + 5) + 5) + 5) looks promising because it equals 23, which is still less than 24. We'll try two ways of getting to 24 from here.
First, by adding 5, we reached a dead end because ((((((1 * 3) + 5) + 5) + 5) + 5) + 5) = 28 which is unfortunately already bigger than 24.
Second, by multiplying by 3, we reached a dead end because ((((((1 * 3) + 5) + 5) + 5) + 5) * 3) = 69 which is unfortunately already bigger than 24.
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from (((((1 * 3) + 5) + 5) + 5) + 5).
Second, by multiplying by 3, we reached a dead end because (((((1 * 3) + 5) + 5) + 5) * 3) = 54 which is unfortunately already bigger than 24.
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from ((((1 * 3) + 5) + 5) + 5).
Second, by multiplying by 3, we reached a dead end because ((((1 * 3) + 5) + 5) * 3) = 39 which is unfortunately already bigger than 24.
Sadly we've exhausted all possible ways of getting there from this starting point. We may still be able to get to 24, but not by starting from (((1 * 3) + 5) + 5).
Second, by multiplying by 3, and guess what...we finally found a solution! Because (((1 * 3) + 5) * 3) = 24. So we can stop now. :)
(((1 * 3) + 5) * 3)