劍指offer33_二叉搜索樹的後序遍歷序列(java)

二叉搜索樹的後序遍歷序列

遞歸地判斷左右區間是否滿足二叉搜索樹的特徵.

public class Solution {
    public boolean VerifySquenceOfBST(int [] sequence) {
        if(sequence == null || sequence.length == 0) return false;
        return help(sequence, 0, sequence.length-1);
    }
    
    // 劃分序列的左右子區間，判斷左右區間是否滿足條件，遞歸的判斷左右子區間的子區間..
    boolean help(int[] sequence, int i,int j){
        boolean flag  = true;
        if(i >= j) return true;
        int p = i;
        while(sequence[p] < sequence[j]) p++;
        int m = p;
        while(sequence[p] > sequence[j]) p++;
        if(p != j) flag = false;
        return flag && help(sequence, i, m-1) && help(sequence, m, j-1);
    }
}