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Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree [1,2,2,3,4,4,3] is symmet 阅读全文
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Given two binary strings, return their sum (also a binary string). The input strings are both non-empty and contains only characters 1 or 0. 以上 阅读全文
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You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you cl 阅读全文
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An array is monotonic if it is either monotone increasing or monotone decreasing. An array A is monotone increasing if for all i <= j, A[i] <= A[j]. A 阅读全文
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Given a non-empty array of digits representing a non-negative integer, plus one to the integer. The digits are stored such that the most significant d 阅读全文
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Given an array nums and a value val, remove all instances of that value in-place and return the new length. Do not allocate extra space for another ar 阅读全文