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118. Pascal's Triangle

1. 问题描述

Given numRows, generate the first numRows of Pascal‘s triangle.

For example, given numRows = 5,

Return
[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]
Tags:Array
Similar Problems:(E) Pascal‘s Triangle II

2. 解题思路


3. 代码

class Solution {public:    vector<vector<int>> generate(int numRows)    {        vector<vector<int>> vResult;        vector<int> vCurRow;        vector<int> vLastRow;        if (numRows <= 0)        {            return vResult;        }        if (1 <= numRows)        {            vCurRow.push_back(1);            vResult.push_back(vCurRow);        }        if (2 <= numRows)        {            vCurRow.push_back(1);            vResult.push_back(vCurRow);        }        vLastRow = vCurRow;        if (3 <= numRows)        {            for (int i=3; i<=numRows; i++)            {                vCurRow.clear();                for (int j=0; j<i; j++)                {                    if (0 == j)                    {                        vCurRow.push_back(1);                    }                    else if (i-1 == j)                    {                        vCurRow.push_back(1);                    }                    else                    {                        int num = vLastRow[j-1] + vLastRow[j];                        vCurRow.push_back(num);                    }                }                vResult.push_back(vCurRow);                vLastRow = vCurRow;            }        }        return vResult;    }};

4. 反思

118. Pascal's Triangle