Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 9 | Sorting and Searching
9.6 Given a matrix in which each row and each column is sorted, write a method to find
an element in it.
SOLUTION
Assumptions:
pg 66
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Rows are sorted left to right in ascending order. Columns are sorted top to bottom in
ascending order.
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Matrix is of size MxN.
This algorithm works by elimination. Every move to the left (--col) eliminates all the elements
below the current cell in that column. Likewise, every move down eliminates all the elements
to the left of the cell in that row.
1 boolean FindElem(int[][] mat, int elem, int M, int N) {
2 int row = 0;
3 int col = N-1;
4 while (row < M && col >= 0) {
5 if (mat[row][col] == elem) {
6 return true;
7 } else if (mat[row][col] > elem) {
8 col--;
9 } else {
10 row++;
11 }
12 }
13 return false;
14 }
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