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35 lines
1.6 KiB
HTML
35 lines
1.6 KiB
HTML
<!DOCTYPE html>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<h1>1086. Tree Traversals Again (25)</h1>
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<div id="problemContent">
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<p>An inorder binary tree traversal can be implemented in a non-recursive way with a stack. For example, suppose that when a 6-node binary tree (with the keys numbered from 1 to 6) is traversed, the stack operations are: push(1); push(2); push(3); pop(); pop(); push(4); pop(); pop(); push(5); push(6); pop(); pop(). Then a unique binary tree (shown in Figure 1) can be generated from this sequence of operations. Your task is to give the postorder traversal sequence of this tree.
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</p>
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<center><img src="http://nos.patest.cn/bs_n9mde9jcnyj.jpg"/><br/>Figure 1</center>
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<p><b>
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Input Specification:
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</b></p>
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<p>Each input file contains one test case. For each case, the first line contains a positive integer N (<=30) which is the total number of nodes in a tree (and hence the nodes are numbered from 1 to N). Then 2N lines follow, each describes a stack operation in the format: "Push X" where X is the index of the node being pushed onto the stack; or "Pop" meaning to pop one node from the stack.</p>
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<p><b>
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Output Specification:
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</b></p>
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<p>For each test case, print the postorder traversal sequence of the corresponding tree in one line. A solution is guaranteed to exist. All the numbers must be separated by exactly one space, and there must be no extra space at the end of the line.
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</p>
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<b>Sample Input:</b><pre>
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6
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Push 1
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Push 2
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Push 3
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Pop
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Pop
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Push 4
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Pop
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Pop
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Push 5
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Push 6
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Pop
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Pop
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</pre>
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<b>Sample Output:</b><pre>
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3 4 2 6 5 1
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</pre>
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</div> |