give m x n matrix mat integer k return matrix answer answerij sum element matrc fori k r kj k c j k andr c valid position matrix Example 1input mat 123456789 k 1Output 122116274533243928example 2input mat 123456789 k 2output 454545454545454545 Constraintsm matlengthn matilength1 m n k 1001 matij 100