118.杨辉三角

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字数统计: 253 | 阅读时长 ≈ 1

题目描述

给定一个非负整数 numRows，生成杨辉三角的前 numRows 行。

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在杨辉三角中，每个数是它左上方和右上方的数的和。

示例:

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输入: 5
输出:
[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

题解

思路

wengcanzi

C:

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/**
 * Return an array of arrays of size *returnSize.
 * The sizes of the arrays are returned as *returnColumnSizes array.
 * Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().
 */
int** generate(int numRows, int* returnSize, int** returnColumnSizes){
    *returnSize = numRows;
    int** res = (int**)malloc(sizeof(int*)*numRows);

    int i;
    for(i = 0; i < numRows; i++){
        (*returnColumnSizes)[i] = i+1;//returnColumnSizes储存杨辉三角每一行元素的个数
        res[i] = (int*)malloc(sizeof(int)*(i+1));
        res[i][0] = 1;
        res[i][i] = 1;
        int j;
        for(j = 1; j < i; j++){
            res[i][j] = res[i-1][j] + res[i-1][j-1];
        }
    }
    return res;
}

思路

取巧解法：错一位再逐个相加

Python:

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class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        if numRows == 0:
            return []
        res = [[1]]
        while len(res) < numRows:
            newRow = [a+b for a, b in zip([0]+res[-1], res[-1]+[0])]
            res.append(newRow)
        return res