Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.
Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example, two is written as II in Roman numeral, just two one’s added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.
Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:
I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.
Example 1:
Input: “III” Output: 3 Example 2:
Input: “IV” Output: 4 Example 3:
Input: “IX” Output: 9 Example 4:
Input: “LVIII” Output: 58 Explanation: L = 50, V= 5, III = 3. Example 5:
Input: “MCMXCIV” Output: 1994 Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
Given two binary trees, write a function to check if they are the same or not.
Two binary trees are considered the same if they are structurally identical and the nodes have the same value.
Example 1:
Input: 1 1 / \ / \ 2 3 2 3
[1,2,3], [1,2,3]
Output: true Example 2:
Input: 1 1 / \ 2 2
[1,2], [1,null,2]
Output: false Example 3:
Input: 1 1 / \ / \ 2 1 1 2
[1,2,1], [1,1,2]
Output: false
Solution
题目其实很简单的一个递归Recursion,我们很轻松可以通过递归来解决
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class Solution { public boolean isSameTree(TreeNode p, TreeNode q) { // p and q are both null if (p == null && q == null) return true; // one of p and q is null if (q == null || p == null) return false; if (p.val != q.val) return false; return isSameTree(p.right, q.right) && isSameTree(p.left, q.left); } }
A straight forward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space, but still not the best solution. Could you devise a constant space solution?
class Solution { public void setZeroes(int[][] matrix) { int R = matrix.length; int C = matrix[0].length; Set<Integer> rows = new HashSet<Integer>(); Set<Integer> cols = new HashSet<Integer>();
for (int i = 0; i < R; i++) { for (int j = 0; j < C; j++) { if (matrix[i][j] == 0) { rows.add(i); cols.add(j); } } }
for (int i = 0; i < R; i++) { for (int j = 0; j < C; j++) { if (rows.contains(i) || cols.contains(j)) { matrix[i][j] = 0; } } } } }
class Solution { public void setZeroes(int[][] matrix) { int R = matrix.length; int C = matrix[0].length; boolean isCol = false; for(int i=0; i<R; i++) { if (matrix[i][0] == 0) { isCol = true; } for(int j=1; j<C; j++) { if(matrix[i][j]==0) { matrix[0][j] = 0; matrix[i][0] = 0; } } } // Iterate over the array once again and using the first row and first column, update the elements. for(int i=1; i<R; i++) { for(int j=1; j<C; j++) { if(matrix[i][0]==0 || matrix[0][j]==0) { matrix[i][j] = 0; } } } // See if the first row needs to be set to zero as well if(matrix[0][0]==0) { for(int j=0; j<C; j++) { matrix[0][j] = 0; } } // See if the first column needs to be set to zero as well if(isCol) { for(int i=0; i<R; i++) { matrix[i][0] = 0; } } } }