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function reverseList(head) {    if (!head || !head.next) return head;    let pre = null;    let current = head;    while (current) {        let next = current.next;        current.next = pre;        pre = current;        current = next;    }    return pre;}

??????????????????????????next?????????next??pre???pre?????????????????????????pre????????????????????

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????????????????????pre-order?????????????????in-order????????????????post-order??????????????

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function kthSmallest(root, k) {    const stack = [];    let result = null;    stack.push(root);    while (stack.length > 0) {        result = stack.pop();        if (result.left) stack.push(result.left);        if (result.right) stack.push(result.right);    }    return result;}

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8 & 7 = 0 // 1000 & 0111 ? 0000

8 | 7 = 15 // 1000 | 0111 ? 1111

8 ^ 7 = 15 // 1000 ^ 0111 ? 1111

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function sum(a, b) {    while (a || b) {        const newA = a ^ b;        const newB = (a & b) << 1;        a = newA;        b = newB;    }    return a;}

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• ??????????? 2*i + 1 ? 2*i + 2????? (i-1)/2?

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function heapify(array, index, size) {    let left = index * 2 + 1;    while (left < size) {        let largest = left + 1 < size && array[left] < array[left + 1] ? left + 1 : left;        if (array[index] < array[largest]) {            swap(array, index, largest);        } else {            break;        }        index = largest;        left = index * 2 + 1;    }}

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function maxDepth(root) {    if (!root) return 0;    return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;}

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function quickSort(arr, left, right) {    if (left >= right) return arr;    let pivot = left;    let partitionIndex = pivot + 1;    for (let i = partitionIndex; i < right; i++) {        if (arr[i] < arr[pivot]) {            swap(arr, i, partitionIndex);            partitionIndex++;        }    }    swap(arr, pivot, partitionIndex - 1);    quickSort(arr, left, partitionIndex - 1);    quickSort(arr, partitionIndex, right);    return arr;}

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