1143. Lowest Common Ancestor (30)

迷南。 2022-05-28 10:25 161阅读 0赞

The lowest common ancestor (LCA) of two nodes U and V in a tree is the deepest node that has both U and V as descendants.

A binary search tree (BST) is recursively defined as a binary tree which has the following properties:

*  The left subtree of a node contains only nodes with keys less than the node's key.
 *  The right subtree of a node contains only nodes with keys greater than or equal to the node's key.
 *  Both the left and right subtrees must also be binary search trees.

Given any two nodes in a BST, you are supposed to find their LCA.

**Input Specification:**

Each input file contains one test case. For each case, the first line gives two positive integers: M (<= 1000), the number of pairs of nodes to be tested; and N (<= 10000), the number of keys in the BST, respectively. In the second line, N distinct integers are given as the preorder traversal sequence of the BST. Then M lines follow, each contains a pair of integer keys U and V. All the keys are in the range of **int**.

**Output Specification:**

For each given pair of U and V, print in a line "LCA of U and V is A." if the LCA is found and A is the key. But if A is one of U and V, print "X is an ancestor of Y." where X is A and Y is the other node. If U or V is not found in the BST, print in a line "ERROR: U is not found." or "ERROR: V is not found." or "ERROR: U and V are not found.".

**Sample Input:**

6 8
    6 3 1 2 5 4 8 7
    2 5
    8 7
    1 9
    12 -3
    0 8
    99 99

**Sample Output:**

LCA of 2 and 5 is 3.
    8 is an ancestor of 7.
    ERROR: 9 is not found.
    ERROR: 12 and -3 are not found.
    ERROR: 0 is not found.
    ERROR: 99 and 99 are not found.

--------------------

题目大意：

代码：

#include<stdio.h>
    #include<map>
    using namespace std;
    int a[100001];
    map<int,int> Map;
    int main()
    {
        int i,j,n,m,k,t,x,y;
        scanf("%d %d",&n,&m);
        for(i=0;i<m;i++)
        {
            scanf("%d",&a[i]);
            Map[a[i]]=1;
        }
        for(i=0;i<n;i++)
        {
            scanf("%d %d",&x,&y);
            if(Map.find(x)==Map.end()&&Map.find(y)==Map.end())
            {
                printf("ERROR: %d and %d are not found.\n",x,y);
            }
            else if(Map.find(x)==Map.end())
            {
                printf("ERROR: %d is not found.\n",x);
            }
            else if(Map.find(y)==Map.end())
            {
                printf("ERROR: %d is not found.\n",y);
            }
            else
            {
                for(j=0;j<m;j++)
                {
                    if((a[j]>x&&a[j]<y)||(a[j]>y&&a[j]<x)||(a[j]==x||a[j]==y))
                    {
                        break;
                    }
                }
                if((a[j]>x&&a[j]<y)||(a[j]>y&&a[j]<x))
                {
                    printf("LCA of %d and %d is %d.\n",x,y,a[j]);
                }
                else if(a[j]==x)
                {
                    printf("%d is an ancestor of %d.\n",x,y);
                }
                else if(a[j]==y)
                {
                    printf("%d is an ancestor of %d.\n",y,x);
                }
            }
        }
        return 0;
    }