标签：bre lse style == lca iostream arch print air
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:
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 99Sample 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.
建树有两种方法，一种是把前序遍历从小到大排序就是中序遍历，然后根据前中序遍历建树。注释部分。
另一种是直接用前序遍历建树。其实中序遍历就是助于判断左右子树，用前序遍历就可以单独判断左右子树的。
代码：
#include <iostream> #include <cstdio> #include <algorithm> #include <map> using namespace std; struct tree { int Data,Height; tree *Last,*Left,*Right; }*head; int q[10001],z[10001],m,n; map<int,tree *> mp; tree *createNode(int d,int h) { tree *p = new tree(); p -> Data = d; mp[d] = p; p -> Height = h; p -> Last = p -> Left = p -> Right = NULL; return p; } tree *createTree(int ql,int qr,int zl,int zr,int h) { tree *p = createNode(q[ql],h); for(int i = zl;i <= zr;i ++) { if(z[i] == q[ql]) { if(i > zl)p -> Left = createTree(ql + 1,ql + i - zl,zl,i - 1,h + 1),p -> Left -> Last = p; if(i < zr)p -> Right = createTree(ql + i - zl + 1,qr,i + 1,zr,h + 1),p -> Right -> Last = p; break; } } return p; } tree *createTre(int l,int r,int h) { tree *p = createNode(q[l],h); for(int i = l + 1;i <= r + 1;i ++) { if(i == r + 1 || q[i] >= q[l]) { if(i > l + 1)p -> Left = createTre(l + 1,i - 1,h + 1),p -> Left -> Last = p; if(r >= i)p -> Right = createTre(i,r,h + 1),p -> Right -> Last = p; return p; } } } void check(int a,int b) { if(mp[a] == NULL && mp[b] == NULL)printf("ERROR: %d and %d are not found.\n",a,b); else if(mp[a] == NULL)printf("ERROR: %d is not found.\n",a); else if(mp[b] == NULL)printf("ERROR: %d is not found.\n",b); else { tree *t1 = mp[a],*t2 = mp[b]; while(t1 -> Height != t2 -> Height) { if(t1 -> Height > t2 -> Height)t1 = t1 -> Last; else t2 = t2 -> Last; } if(t1 == t2) { printf("%d is an ancestor of %d.\n",t1 -> Data,a == t1 -> Data ? b : a); return; } t1 = t1 -> Last; t2 = t2 -> Last; while(t1 != t2) { t1 = t1 -> Last; t2 = t2 -> Last; } printf("LCA of %d and %d is %d.\n",a,b,t1 -> Data); } } int main() { int a,b; scanf("%d%d",&m,&n); for(int i = 0;i < n;i ++) { scanf("%d",&q[i]); //z[i] = q[i]; } //sort(z,z + n); // head = createTree(0,n - 1,0,n - 1,0); head = createTre(0,n - 1,0); for(int i = 0;i < m;i ++) { scanf("%d%d",&a,&b); check(a,b); } }
1143. Lowest Common Ancestor (30)
标签：bre lse style == lca iostream arch print air
原文地址：https://www.cnblogs.com/8023spz/p/8976489.html
