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public class Solution { public int[] twoSum(int[] numbers, int target) { // IMPORTANT: Please reset any member data you declared, as ... 阅读全文
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Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.For example:Given the below binary tree andsum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ ... 阅读全文
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/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { * val = x; * next = null; * } * } */public class Solution { public ListNode mergeTwoLists(ListNode l1, ListNode l2) { if(l1 == null) return l2;... 阅读全文
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递归解法/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */public class Solution { public boolean isValidBST(TreeNode root) { return isValidBSTHelper(root, Integer.MIN_VALUE, Integer.MAX_... 阅读全文
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Given a binary tree, determine if it is height-balanced.For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees ofeverynode never differ by more than 1./** * Definition for binary tree * public class TreeNode { * int val; * TreeNode ... 阅读全文
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Given two sorted integer arrays A and B, merge B into A as one sorted array.Note:You may assume that A has enough space to hold additional elements from B. The number of elements initialized in A and B aremandnrespectively.public class Solution { public void merge(int A[], int m, int B[], int n) ... 阅读全文
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参考：http://www.cnblogs.com/reynold-lei/p/3385290.html http://www.cnblogs.com/feiling/p/3302242.html罗马数字共有7个，即I（1）、V（5）、X（10）、L（50）、C（100）、D（500）和M（1000）。在较大的罗马数字的右边记上较小的罗马数字，表示大数字加小数字。在较大的罗马数字的左边记上较小的罗马数字，表示大数字减小数字。左减的数字有限制，仅限于I、X、C。比如45不可以写成VL，只能是XLV但是，左减时不可跨越一个位数。比如，99不可以用IC（）表示，而是用XCIX（）表示。（等同于阿拉. 阅读全文
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Given a sorted array of integers, find the starting and ending position of a given target value.Your algorithm's runtime complexity must be in the order ofO(logn).If the target is not found in the array, return[-1, -1].For example,Given[5, 7, 7, 8, 8, 10]and target value 8,return[3, 4].public cl 阅读全文
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参考 http://fisherlei.blogspot.com/2012/12/leetcode-largest-rectangle-in-histogram.html以下摘自水中的鱼：这样的话，就可以通过大数据。但是这个优化只是比较有效的剪枝，算法仍然是O(n*n).想了半天，也想不出来O(n)的解法，于是上网google了一下。如下图所示，从左到右处理直方，i=4时，小于当前栈顶（及直方3），于是在统计完区间[2,3]的最大值以后，消除掉阴影部分，然后把红线部分作为一个大直方插入。因为，无论后面还是前面的直方，都不可能得到比目前栈顶元素更高的高度了。这就意味着，可以维护一个递增的栈，每次 阅读全文
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Trapping Rain WaterGiven n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.For example,Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6.The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In 阅读全文