medium10 pts · first answer countsarraysprefix-sumsmatrix

Rectangle sum from a 2D prefix table

P[i][j] is the sum of cells above and left of (i, j), exclusive, with an extra zero row and column. Which formula gives the sum of rows r1..r2 and columns c1..c2?

A.P[r2+1][c2+1] - P[r1][c1]B.P[r2+1][c2+1] - P[r1][c2+1] - P[r2+1][c1] + P[r1][c1]C.P[r2][c2] - P[r1][c2] - P[r2][c1] - P[r1][c1]D.P[r2+1][c2+1] - P[r1][c2+1] - P[r2+1][c1]

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Rectangle sum from a 2D prefix table

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