Sum of Both Diagonals

Easy

You are given a square n × n matrix grid. Add up every number on the main diagonal (top-left to bottom-right) and on the anti-diagonal (top-right to bottom-left). When n is odd, the two diagonals meet in the centre cell; count its value only once. Return the total.

Example 1

grid=[[2, 4, 6], [1, 3, 5], [8, 7, 9]] → 28

Main diagonal: 2 + 3 + 9; anti-diagonal: 6 + 8 (the centre 3 is already counted). Total 28.

Example 2

grid=[[1, 2], [3, 4]] → 10

In a 2×2 grid the diagonals do not cross: 1 + 4 + 2 + 3 = 10.

Example 3

grid=[[7]] → 7

Constraints

n == len(grid) == len(grid[i])
1 ≤ n ≤ 100
1 ≤ grid[i][j] ≤ 100

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Topics

Array Matrix

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Input

grid=[[2, 4, 6], [1, 3, 5], [8, 7, 9]]

Expected

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