[数据结构与算法]C语言数据结构，二叉树的应用

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<ctype.h>
#define MAX_LEN 5
typedef struct node {
char optr;
int data;
struct node* lchild;
struct node* rchild;
}BTNode;
BTNode* getNode(char* str, int& pos) {
BTNode* createTree(char* str, int& pos);
BTNode* p = new BTNode;
char ch = str[0];
if (isdigit(ch)) {
int i = 0;
char data[MAX_LEN];
while (isdigit(ch = str[i]))
data[i++] = ch;
p->data = atoi(data);
pos += i;
}
else if (ch == ‘+’ || ch == ‘-’ || ch == ‘’ || ch == ‘/’) {
p->optr = ch;
pos += 1;
p = createTree(str + 1, pos);
}
else if (ch == ‘)’) {
pos += 1;
return NULL;
}
else if (ch == ‘\0’)
return NULL;
return p;
}
int getPriority(char optr) {
switch (optr) {
case’+’:
case’-’:
return 1;
case’’:
case’/’:
return 2;
}
return 0;
}
BTNode* createTree(char* str, int& pos) {
int pos1 = 0;
BTNode* lchild = getNode(str + pos1, pos1);
BTNode* root = getNode(str + pos1, pos1);
BTNode* rchild = getNode(str + pos1, pos1);
root->lchild = lchild;
root->rchild = rchild;
BTNode* node;
while ((node = getNode(str + pos1, pos1))) {
if (getPriority(root->optr) > getPriority(node->optr)) {
node->lchild = root;
node->rchild = getNode(str + pos1, pos1);
root = node;
}
else {
node->lchild = root->rchild;
root->rchild = node;
node->rchild = getNode(str + pos1, pos1);
}
}
pos += pos1;
return root;
}
int result(BTNode* b) {
int n1, n2;
switch (b->optr) {
case’+’:
n1 = result(b->lchild);
n2 = result(b->rchild);
b->data = n1 + n2;
break;
case’-’:
n1 = result(b->lchild);
n2 = result(b->rchild);
b->data = n1 - n2;
break;
case’*’:
n1 = result(b->lchild);
n2 = result(b->rchild);
b->data = n1 * n2;
break;
case’/’:
n1 = result(b->lchild);
n2 = result(b->rchild);
b->data = n1 / n2;
break;
default:
return b->data;
}
return b->data;
}

int main() {
BTNode* b = NULL, * q = NULL;
char str[100];
printf(“请输入符合要求的代数表达式:”);
scanf("%s", str);
int n = 0, i = 0;
while (str[i++] != ‘\0’)
n++;
int pos = 0;
b = createTree(str, pos);
printf(“该表达式的值为:%d\n”, result(b));
}