Given a rows x cols matrix mat, where mat[i][j] is either 0 or 1, return the number of special positions in mat. A position (i,j) is called special if mat[i][j] == 1 and all other elements in row i and column j are 0 (rows and columns are 0-indexed). Example 1: Input: mat = [[1,0,0], [0,0,1], [1,0,0]] Output: 1 Explanation: (1,2) is a special position because mat[1][2] == 1 and all other elements in row 1 and column 2 are 0. Example 2: Input: mat = [[1,0,0], [0,1,0], [0,0,1]] Output: 3 Explanation: (0,0), (1,1) and (2,2) are special positions. Example 3: Input: mat = [[0,0,0,1], [1,0,0,0], [0,1,1,0], [0,0,0,0]] Output: 2 Example 4: Input: mat = [[0,0,0,0,0], [1,0,0,0,0], [0,1,0,0,0], [0,0,1,0,0], [0,0,0,1,1]] Output: 3 Constraints: rows == mat.length cols == mat[i].length 1 <= rows, cols <= 100 mat[i][j] is 0 or 1.