1572.Matrix Diagonal Sum

tags: Easy,Array,Matrix

1572. Matrix Diagonal Sum

題目描述

Given a square matrix mat, return the sum of the matrix diagonals.

Only include the sum of all the elements on the primary diagonal and all the elements on the secondary diagonal that are not part of the primary diagonal.

範例

Example 1:

Input: mat = [[1,2,3],
              [4,5,6],
              [7,8,9]]
Output: 25
Explanation: Diagonals sum: 1 + 5 + 9 + 3 + 7 = 25
Notice that element mat[1][1] = 5 is counted only once.

Example 2:

Input: mat = [[1,1,1,1],
              [1,1,1,1],
              [1,1,1,1],
              [1,1,1,1]]
Output: 8

Example 3:

Input: mat = [[5]]
Output: 5

Constraints:

• n == mat.length == mat[i].length
• 1 <= n <= 100
• 1 <= mat[i][j] <= 100

解答

Python

class Solution:
    def diagonalSum(self, mat: List[List[int]]) -> int:
        n = len(mat)
        ans = 0
        for i in range(n):
            ans += mat[i][i] + mat[i][n - i - 1]
        if n & 1:
            ans -= mat[n // 2][n // 2]
        return ans

Yen-Chi ChenMon, May 8, 2023

class Solution:
    def diagonalSum(self, mat: List[List[int]]) -> int:
        return sum([mat[i][i] + mat[i][len(mat) - i - 1] if i != len(mat) - i - 1 else mat[i][i] for i in range(len(mat))])

Ron ChenMon, May 8, 2023

Javascript

function diagonalSum(mat) {
  let sum = 0;
  const n = mat.length - 1;
  for (let i = 0; i <= n; i++) {
    for (let j = 0; j <= n; j++) {
      if (i === j || n - i === j || n - j === i) {
        sum += mat[i][j];
      }
    }
  }

  return sum;
}

MarsgoatMon, May 8, 2023

TypeScript

function diagonalSum(mat: number[][]): number {
  const matLength = mat.length;
  const midIndex = ~~(matLength / 2);
  let primarySum = 0;
  let secondarySum = 0;

  for (let i = 0; i < matLength; i++) {
    primarySum += mat[i][i];
    secondarySum += mat[i][matLength - 1 - i];
  }

  return matLength % 2
    ? primarySum + secondarySum - mat[midIndex][midIndex]
    : primarySum + secondarySum;
}

SheepMon, May 8, 2023

Reference

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