我有以下代码:
class TreeNode {
constructor(val) {
this.val = val
this.left = this.right = null
}
}
const isSymmetric = root => {
if (!root) return true
let stackP = []
let stackQ = []
let currentP = root
let currentQ = root
while ((currentP && currentQ) || (stackP.length && stackQ.length)) {
while (currentP) {
stackP.push(currentP)
currentP = currentP.left
}
while (currentQ) {
stackQ.push(currentQ)
currentQ = currentQ.right
}
console.log(stackP, stackQ, 'after push')
currentP = stackP.pop()
currentQ = stackQ.pop()
console.log(stackP, stackQ, 'after 1 iterative pop')
if ((currentP.val !== currentQ.val) || (stackP.length !== stackQ.length)) return false
console.log(currentP, currentQ, 'after if statement')
// confused as to why we are setting it to the opposite here
currentP = currentP.right
currentQ = currentQ.left
console.log(currentP, currentQ, 'after opp DECLARATION')
}
return true
}
//example 1
const tree1 = new TreeNode(1)
tree1.left = new TreeNode(2)
tree1.right = new TreeNode(2)
tree1.left.left = new TreeNode(3)
tree1.left.right = new TreeNode(4)
tree1.right.left = new TreeNode(4)
tree1.right.right = new TreeNode(3)
//example 2
const tree2 = new TreeNode(1)
tree2.left = new TreeNode(2)
tree2.right = new TreeNode(2)
tree2.left.right = new TreeNode(3)
tree2.right.right = new TreeNode(3)
console.log(isSymmetric(tree1));
console.log(isSymmetric(tree2));
但是,我对以下两行感到困惑:
currentP = currentP.right
currentQ = currentQ.left
我不知道为什么要这样做。我尝试跟随控制台日志记录,但无法跟随。我希望 currentP
能够遵循设置在左侧的原始模式来维持自身,但在弹出 P
和 Q
后,它们似乎是现在向右移动。我不明白为什么。谁能解释一下吗?
假设我们有以下树
A
/ \
B B
/ \ / \
C D D C
跟踪currentP
和currentQ
应该给出以下值A、B、C、C、null、B、D、null、A。但是当我们到达A时从逻辑上看,我们似乎处于无限循环中。除非我没有正确跟踪它。在我们将 currentP
和 currentQ
声明为“A”之后,我们应该再次进入 while 循环,本质上是再次将 B 和 C 推回去,我是否错过了什么?
最佳答案
给定这棵树:
A
/ \
B C
/ \ / \
D E F G
首先,它一直向左(stackP = B,D)堆叠它们,然后向右(stackQ = C,G)。然后比较最后的叶子(D,G)。然后拿他们的 sibling (E,F)进行比较 - 这就是您正在谈论的部分。然后弹出他们的 parent (B,C)并进行比较。
这是带有一些调试信息的程序,可以让您更好地了解它正在做什么:
class TreeNode {
constructor(val) {
this.val = val;
this.left = this.right = null;
}
}
function serialize(arr) {
return arr.map(e => e.val).join(",");
}
const isSymmetric = (root) => {
if (!root) return true;
let stackP = [];
let stackQ = [];
let currentP = root;
let currentQ = root;
while ((currentP && currentQ) || (stackP.length && stackQ.length)) {
while (currentP) {
stackP.push(currentP);
console.log(`Pushing ${currentP.val} to sP=[${serialize(stackP)}]`)
currentP = currentP.left;
}
while (currentQ) {
stackQ.push(currentQ);
console.log(`Pushing ${currentQ.val} to sQ=[${serialize(stackQ)}]`)
currentQ = currentQ.right;
}
currentP = stackP.pop();
currentQ = stackQ.pop();
console.log(`Comparing cP=${currentP.val} cQ=${currentQ.val} sP=[${serialize(stackP)}] sQ=[${serialize(stackQ)}]`);
if (currentP.val !== currentQ.val || stackP.length !== stackQ.length)
return false;
// confused as to why we are setting it to the opposite here
currentP = currentP.right;
currentQ = currentQ.left;
console.log(`Looping cP=${currentP ? currentP.val : "null"} cQ=${currentQ ? currentQ.val : "null"} sP=[${serialize(stackP)}] sQ=[${serialize(stackQ)}]`);
}
return true;
};
//example 1
const tree1 = new TreeNode(1)
tree1.left = new TreeNode(2)
tree1.right = new TreeNode(2)
tree1.left.left = new TreeNode(3)
tree1.left.right = new TreeNode(4)
tree1.right.left = new TreeNode(4)
tree1.right.right = new TreeNode(3)
//example 2
const tree2 = new TreeNode(1)
tree2.left = new TreeNode(2)
tree2.right = new TreeNode(2)
tree2.left.right = new TreeNode(3)
tree2.right.right = new TreeNode(3)
console.log(isSymmetric(tree1));
console.log(isSymmetric(tree2));
关于javascript - 我正在寻找检查树是否对称的迭代解决方案,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/61112735/