构造只给出后序的全二叉树？

Question

2(1.000000e+00)
3(1.000000e+00)
(1.000000e+00 1.000000e+00)
1(1.000000e+00)
(1.000000e+00 2.000000e+00)

Node *constructTreeHelper(FILE *infile, int *index) { 
    // Base case 
    if (*index <= 0) {
        return NULL; 
    }
    Node *root = NULL;

    // Check for the "(" character
    int check;
    check = getc(infile);
    fseek(infile, -1, SEEK_CUR);

    // If the node is not a leaf node
    if (check == 40) {
        double lwire, rwire;
        fscanf(infile, "(%le %le)\n", &lwire, &rwire);
        root = createNode(0, 0, lwire, rwire);
        *index = *index - 1;
        if (*index >= 0) { 
            root->right = constructTreeHelper(infile, index); 
            root->left = constructTreeHelper(infile, index); 
        } 
    } else {
        // If the node is a leaf node
        int sink;
        double cap;
        fscanf(infile, "%d(%le)\n", &sink, &cap);
        root = createNode(sink, cap, 0, 0);
        *index = *index - 1;
        if (*index >= 0) { 
            root->right = constructTreeHelper(infile, index); 
            root->left = constructTreeHelper(infile, index); 
        } 
    }
    return root;
} 

Answer 1

您的代码中存在一些问题：

>

您应该使用ungetc()而不是fseek()返回一个字符，以避免不支持查找的流出现故障。

您应该编写(check=='(')，而不是硬编码ASCII字符值，这样既可移植又更易读。

当您解析叶节点时，您不应该递归和解析当前节点下面的更多节点。

index似乎是多余的，因为节点序列应该足以完全确定停止的位置。

下面是一个修改版本：

Node *constructTreeHelper(FILE *infile, int *index) { 
    double lwire, rwire;
    int sink;
    double cap;
    Node *node;

    // Base case 
    if (*index <= 0) {
        // This test seems redundant with the file contents */
        return NULL; 
    }

    // this fscanf will fail on the byte byte if it is not a '('
    if (fscanf(infile, " (%le %le)", &lwire, &rwire) == 2) {
       // If the node is not a leaf node
        node = createNode(0, 0, lwire, rwire);
        *index -= 1;
        node->right = constructTreeHelper(infile, index); 
        node->left = constructTreeHelper(infile, index); 
    } else if (fscanf(infile, "%d(%le)\n", &sink, &cap) == 2) {
        // If the node is a leaf node
        node = createNode(sink, cap, 0, 0);
        *index -= 1;
    } else {
        // invalid format or end of file */
        node = NULL;
    }
    return node;
}