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//2020-04-30//注意c的结构体赋值并非是传递结构体的引用（指针）//js和Java写多了容易漏掉这个东西/*** 后序遍历：当返回根结点时需要判断是左孩子还是右孩子返回，两种实现方式：* 1.使用变量记录上一次访问的结点* 2.创建新的结构，添加tag字段标识结点的左右孩子是否访问，当进入根节点的左右孩子时，无论此时左右是否被访问，* 都应该设置相应的标志，因为当左右孩子返回根结点时，返回的孩子分支树一定已经被访问过了， 当访问了右孩子时其左孩子一定被访问*/#include#include #define MAX 100#define LEFT 0#define RIGHT 1typedef int Elem;typedef struct BTNode { Elem e; struct BTNode * lChild; struct BTNode * rChild;} * BTNode;typedef struct { BTNode node; //标识当前节点是否被访问 int tag;} TNode;BTNode ancestor(BTNode root, Elem p, Elem q);BTNode buildTree(Elem [], int , int , Elem [], int , int );void preOrder(BTNode);void inOrder(BTNode);void postOrder(BTNode);int i = 1;int main(void) { Elem A[] = { 1,2,4,5,3,6,7}; Elem B[] = { 4,2,5,1,6,3,7}; BTNode obj = buildTree(A, 0, 6, B, 0, 6); postOrder(obj); //printf("%d", ancestor(obj, 4, 6)->e); return 0; } BTNode ancestor(BTNode root, Elem p, Elem q) { TNode stack[MAX], ancestor[MAX]; int top = -1, top_a = -1; while(root != NULL || top > -1) { if(root) { stack[++top] = (TNode){ root, LEFT}; root = root->lChild; } else { TNode t = stack[top]; if(t.node->rChild && t.tag == LEFT) { t.tag = RIGHT; root = root->rChild; } else { --top; if(t.node->e == p) { while(top_a < top) { top_a++; ancestor[top_a] = stack[top_a]; } } else if(t.node->e == q) { break; } root = NULL; } } } int i = 0; while(stack[i].node == ancestor[i].node) ++i; return stack[--i].node; }BTNode buildTree(Elem A[], int sa, int ea, Elem B[], int sb, int eb) { BTNode node = (BTNode)malloc(sizeof(struct BTNode) * 1); node->e = A[sa]; int i = sb; for(i; A[sa] != B[i]; ++i); int ll = i - sb; int rr = eb - i; if(ll > 0) { node->lChild = buildTree(A, sa + 1, sa + ll, B, sb, sb + ll - 1); } else { node->lChild = NULL; } if(rr > 0) { node->rChild = buildTree(A, sa + ll + 1, ea, B, sb + ll + 1, eb); } else { node->rChild = NULL; } return node;}void preOrder(BTNode T) { if(T == NULL) return; printf("%d ", T -> e); preOrder(T->lChild); preOrder(T->rChild);}void inOrder(BTNode T) { if(T == NULL) return; inOrder(T->lChild); printf("%d ", T -> e); inOrder(T->rChild);}void postOrder(BTNode T) { TNode * stack[MAX]; BTNode root = T; int top = -1; while(root != NULL || top > -1) { if(root ) { TNode * t = (TNode *)malloc(sizeof(TNode)); t->node = root; t->tag = LEFT; stack[++top] = t; root = root->lChild; } else { TNode * t = stack[top]; if(t->node->rChild != NULL && t->tag == LEFT) { t->tag = RIGHT; root = t->node->rChild; } else { --top; printf("%d ", t->node->e); root = NULL; } } } }
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