evaluate-reverse-polish-notation

题目描述

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are+,-,*,/. Each operand may be an integer or another expression.

Some examples:

["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9

["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

/**
 * @author gentleKay
 * Given a binary tree, find its minimum depth.   给定二叉树，求其最小深度。
 * The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
 * 最小深度是从根节点到最近的叶节点沿最短路径的节点数。
 */

public class Main01 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TreeNode root = new TreeNode(4);
		root.left = new TreeNode(2);
		root.left.left = new TreeNode(1);
		root.left.right  = new TreeNode(3);
		
		root.right = new TreeNode(6);
		root.right.left = new TreeNode(5);
		root.right.right = new TreeNode(7);
		root.right.right.right = new TreeNode(8);
		System.out.println(Main01.run(root));
	}
	
	public static class TreeNode {
		int val;
		TreeNode left;
		TreeNode right;
		TreeNode(int x) { val = x; }
	}
	
	public static int run(TreeNode root) {
		
		if (root == null) {
			return 0;
		}
		if (root.left == null) {
			return run(root.right) + 1;
		}
		
		if (root.right == null) {
			return run(root.left) + 1;
		}
		return Math.min(run(root.left)+1, run(root.right)+1);
    }
}

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