二叉树中找两个结点的最近公共祖先结点

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解题思路

1. 计算两个节点到最终祖先的距离
2. 根据这两个距离让两个节点来到同一高度
3. 然后直接一步一步网上找公共祖先

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代码

import java.util.*;
//二叉树
class TreeNode {
    int val;
    TreeNode father;
    TreeNode lchild;
    TreeNode rchild;

    public TreeNode(int val) {
        this.val = val;
    }
}

public class Main {

    public static TreeNode findTheirFather(TreeNode node1, TreeNode node2) {
        int pathlen1 = 0, pathlen2 = 0;

        //计算node1到最终祖先的距离
        TreeNode temp = node1;
        while(temp.father != null) {
            pathlen1++;
            temp = temp.father;
        }

        //计算node2到最终祖先的距离
        temp = node2;
        while(temp.father != null) {
            pathlen2++;
            temp = temp.father;
        }

        //让node1和node2来到同一高度
        int pathlen11 = pathlen1, pathlen22 = pathlen2;
        //计算node1和node2需要走的距离
        pathlen11 = pathlen11 - Math.min(pathlen1, pathlen2);
        pathlen22 = pathlen22 - Math.min(pathlen1, pathlen2);
        while(pathlen11 > 0) {
            pathlen11--;
            node1 = node1.father;
        }
        while(pathlen22 > 0) {
            pathlen22--;
            node2 = node2.father;
        }

        //从同一高度找最近公共祖先
        while(node1 != node2) {
            node1 = node1.father;
            node2 = node2.father;
        }
        return node1;
    }

    //测试
    public static void main(String[] args) {

    }
}