4.7---最近公共祖先（CC150）

import java.util.*;

public class LCA {

    public static int getLCA(int a, int b){
            if(a < 1 || b < 1){
                return -1;
            }
            if(a == b) return a;

            while(a != b){
                if(a > b){
                    a = a/2;
                }
                else{
                    b = b/2;
                }
            }
            return a;
        }
}
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