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			23 lines
		
	
	
		
			588 B
		
	
	
	
		
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<p>三步问题。有个小孩正在上楼梯,楼梯有n阶台阶,小孩一次可以上1阶、2阶或3阶。实现一种方法,计算小孩有多少种上楼梯的方式。结果可能很大,你需要对结果模1000000007。</p>
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<p> <strong>示例1:</strong></p>
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<pre>
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<strong> 输入</strong>:n = 3 
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<strong> 输出</strong>:4
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<strong> 说明</strong>: 有四种走法
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</pre>
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<p> <strong>示例2:</strong></p>
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<pre>
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<strong> 输入</strong>:n = 5
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<strong> 输出</strong>:13
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</pre>
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<p> <strong>提示:</strong></p>
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<ol>
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<li>n范围在[1, 1000000]之间</li>
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</ol>
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