?LeetCode刷題實戰(zhàn)331：驗證二叉樹的前序序列化

示例 1:

輸入: "9,3,4,#,#,1,#,#,2,#,6,#,#"
輸出: true

示例 2:

輸入: "1,#"
輸出: false

示例 3:

輸入: "9,#,#,1"
輸出: false

class Solution {
    public boolean isValidSerialization(String preorder) {
        int n = preorder.length();
        int i = 0;
        Deque<Integer> stack = new LinkedList<Integer>();
        stack.push(1);
        while (i < n) {
            if (stack.isEmpty()) {
                return false;
            }
            if (preorder.charAt(i) == ',') {
                i++;
            } else if (preorder.charAt(i) == '#'){
                int top = stack.pop() - 1;
                if (top > 0) {
                    stack.push(top);
                }
                i++;
            } else {
                // 讀一個數(shù)字
                while (i < n && preorder.charAt(i) != ',') {
                    i++;
                }
                int top = stack.pop() - 1;
                if (top > 0) {
                    stack.push(top);
                }
                stack.push(2);
            }
        }
        return stack.isEmpty();
    }
}

作者：LeetCode-Solution
鏈接：https://leetcode-cn.com/problems/verify-preorder-serialization-of-a-binary-tree/solution/yan-zheng-er-cha-shu-de-qian-xu-xu-lie-h-jghn/
來源：力扣（LeetCode）
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