力扣——449. 序列化和反序列化二叉搜索树（Java、C代码实现）

449. 序列化和反序列化二叉搜索树
     序列化是将数据结构或对象转换为一系列位的过程，以便它可以存储在文件或内存缓冲区中，或通过网络连接链路传输，以便稍后在同一个或另一个计算机环境中重建。

设计一个算法来序列化和反序列化 二叉搜索树 。 对序列化/反序列化算法的工作方式没有限制。 您只需确保二叉搜索树可以序列化为字符串，并且可以将该字符串反序列化为最初的二叉搜索树。

编码的字符串应尽可能紧凑。

示例 1：

输入：root = [2,1,3]
输出：[2,1,3]
示例 2：

输入：root = []
输出：[]

Java代码：

public class Codec {
    public String serialize(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        postOrder(root, list);
        String str = list.toString();
        return str.substring(1, str.length() - 1);
    }

    public TreeNode deserialize(String data) {
        if (data.isEmpty()) {
            return null;
        }
        String[] arr = data.split(", ");
        Deque<Integer> stack = new ArrayDeque<Integer>();
        int length = arr.length;
        for (int i = 0; i < length; i++) {
            stack.push(Integer.parseInt(arr[i]));
        }
        return construct(Integer.MIN_VALUE, Integer.MAX_VALUE, stack);
    }

    private void postOrder(TreeNode root, List<Integer> list) {
        if (root == null) {
            return;
        }
        postOrder(root.left, list);
        postOrder(root.right, list);
        list.add(root.val);
    }

    private TreeNode construct(int lower, int upper, Deque<Integer> stack) {
        if (stack.isEmpty() || stack.peek() < lower || stack.peek() > upper) {
            return null;
        }
        int val = stack.pop();
        TreeNode root = new TreeNode(val);
        root.right = construct(val, upper, stack);
        root.left = construct(lower, val, stack);
        return root;
    }
}

C代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

struct TreeNode *tree_node(int val) {
    struct TreeNode *node = (struct TreeNode *) malloc(sizeof(struct TreeNode));
    node->val = val;
    node->left = NULL;
    node->right = NULL;
    return node;
}

#define MAXN 10000

/* Generate the pre-order string.
   Nodes are separated by '_'. */
void genstr(struct TreeNode *root, char **strp) {
    if (root == NULL) {
        return;
    }
    char buf[32];
    sprintf(buf, "%d_", root->val);
    strcat(*strp, buf);
    genstr(root->left, strp);
    genstr(root->right, strp);
}

/* Transfer the serialize string to integer array. */
int *get_vals(char *str, int *retsz) {
    int n = strlen(str);
    int *vals = (int *) malloc(MAXN * sizeof(int));
    *retsz = 0;
    char *cp = str;
    for (int i = 0; i < n; i++) {
        if (str[i] != '_')
            continue;
        str[i] = '\0';
        vals[(*retsz)++] = atoi(cp);
        cp = str + i + 1;
    }
    return vals;
}

/* Generate BST according to the pre-order values array. */
struct TreeNode *gentree(int *vals, int l, int r) {
    if (l > r)
        return NULL;
    if (l == r)
        return tree_node(vals[l]);
    struct TreeNode *root = tree_node(vals[l]);

    /* Find the index of the first value which
       larger than [root->val] by binary search. */
    int i = l + 1, j = r, mid, index = r + 1;
    while (i <= j) {
        mid = i + (j - i >> 1);
        if (vals[mid] >= root->val) {
            index = mid;
            j = mid - 1;
        } else {
            i = mid + 1;
        }
    }

    root->left = gentree(vals, l + 1, index - 1);
    root->right = gentree(vals, index, r);
    return root;
}

/** Encodes a tree to a single string. */
char *serialize(struct TreeNode *root) {
    char *str = (char *) calloc(5 * MAXN + 1, 1);
    genstr(root, &str);
    return str;
}

/** Decodes your encoded data to tree. */
struct TreeNode *deserialize(char *data) {
    int *vals, vals_size;
    struct TreeNode *root;
    vals = get_vals(data, &vals_size);
    root = gentree(vals, 0, vals_size - 1);
    free(vals);
    return root;
}

// Your functions will be called as such:
// char* data = serialize(root);
// deserialize(data);

作者：KJ.JK
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