剑指offer之 二叉搜索树的后续遍历序列

Posted 2020-10-10 toov5

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。如果是则输出Yes,否则输出No。假设输入的数组的任意两个数字都互不相同。

 

public class Solution {
    public boolean VerifySquenceOfBST(int [] sequence) {
        if(sequence.length == 0) return false;
        return IsTreeBST(sequence, 0, sequence.length-1);
    }
    public boolean IsTreeBST(int [] sequence,int start,int end ){
        //if(end <= start) return true;
        int i = start;
        for (; i < end; i++) {
            if(sequence[i] > sequence[end]) break;
        }
        int j;
        for (j = i; j < end; j++) {
            if(sequence[j] < sequence[end]) return false;
        }
        boolean left=true;
        //根结点左子树不为空
        if(i>0){
            left=IsTreeBST(sequence, start, i-1);
        }
        boolean right=true;
        //根结点右子树不为空
        if(j<end-1){
            return IsTreeBST(sequence, i, end-1);
        }
        return left&&right;
    }
}