zoukankan      html  css  js  c++  java
  • leetcode 119. Pascal's Triangle II

    Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal's triangle.

    Note that the row index starts from 0.


    In Pascal's triangle, each number is the sum of the two numbers directly above it.

    Example:

    Input: 3
    Output: [1,3,3,1]
    

    Follow up:

    Could you optimize your algorithm to use only O(k) extra space?

    class Solution:
        def getRow(self, rowIndex):
            """
            :type rowIndex: int
            :rtype: List[int]
            """
            start = ans = [1]
            for i in xrange(0, rowIndex):            
                ans = start + [1]
                for j in xrange(1, len(ans)-1):
                    ans[j] = start[j]+start[j-1]
                start = ans
            return ans
    

    还可以少一个临时变量,从后向前计算相加:

    class Solution:
        def getRow(self, rowIndex):
            """
            :type rowIndex: int
            :rtype: List[int]
            """
            ans = [1]
            for i in xrange(0, rowIndex):            
                ans = ans + [1]
                for j in xrange(len(ans)-2, 0, -1):
                    ans[j] = ans[j]+ans[j-1]            
            return ans
    

    也有使用dummy变量的做法:

    class Solution(object):
        def getRow(self, rowIndex):
            """
            :type rowIndex: int
            :rtype: List[int]
            """
            row = [1]
            for _ in range(rowIndex):
                row = [x + y for x, y in zip([0]+row, row+[0])]
            return row
    

     另外就是数学解法,没有懂,TODO:

    class Solution {
    public:
        vector<int> getRow(int k) {
            vector<int> ans(k+1,1);
            for(int i=1;i<=k/2;++i){          
               ans[k-i]= ans[i]=long(ans[i-1])*(k-i+1)/i;           
            }        
            return ans;
        }
    };
    
  • 相关阅读:
    EOJ 1822 Hanoi Tower IV
    Firefox,chrome,IE上传图片预览
    js保存,获取,删除cookie的操作
    jquery 特效
    SimpleDateFormat转换时间,12,24时间格式[转]
    javascript捕获页面窗口关闭事件
    [转]ajQuery的deferred对象详解
    iframe
    火狐路径问题
    JAVA折腾微信公众平台(Token验证)[转]
  • 原文地址:https://www.cnblogs.com/bonelee/p/9180711.html
Copyright © 2011-2022 走看看