JZ-023-Post-order traversal sequence of binary search tree

Post-order traversal sequence of binary search tree

Title description

Enter an integer array to determine whether the array is the result of a post-order traversal of a binary search tree. If it is, it returns true, otherwise it returns false. Assume that any two numbers in the input array are different from each other.

topic link : post-order traversal sequence of binary search tree

Code

/**
 * 标题：二叉搜索树的后序遍历序列
 * 题目描述
 * 输入一个整数数组，判断该数组是不是某二叉搜索树的后序遍历的结果。如果是则返回true,否则返回false。假设输入的数组的任意两个数字都互不相同。
 * 题目链接：
 * https://www.nowcoder.com/practice/a861533d45854474ac791d90e447bafd?tpId=13&&tqId=11176&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz23 {

    public boolean verifySquenceOfBST(int[] sequence) {
        if (sequence == null || sequence.length == 0) {
            return false;
        }
        return verify(sequence, 0, sequence.length - 1);
    }

    /**
     * 递归法
     *
     * @param sequence
     * @param first
     * @param last
     * @return
     */
    private boolean verify(int[] sequence, int first, int last) {
        if (last - first <= 1) {
            return true;
        }
        int rootVal = sequence[last];
        int cutIndex = first;
        while (cutIndex < last && sequence[cutIndex] <= rootVal) {
            cutIndex++;
        }
        for (int i = cutIndex; i < last; i++) {
            if (sequence[i] < rootVal) {
                return false;
            }
        }
        return verify(sequence, first, cutIndex - 1) && verify(sequence, cutIndex, last - 1);
    }

    public static void main(String[] args) {

    }
}

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