0074-search-a-2d-matrix.java

//Similar to binary search in 1D array, here the search space is from (0,0) to (m-1,n-1)
class Solution {

    public boolean searchMatrix(int[][] matrix, int target) {
        int i = 0, j = matrix[0].length - 1;
        while (i < matrix.length && j >= 0) {
            if (matrix[i][j] == target) return true; else if (
                matrix[i][j] > target
            ) j--; else i++;
        }
        return false;
    }

    //    Time: O(log(mn)) | Space: O(1)
    public boolean searchMatrix2(int[][] matrix, int target) {
        if(matrix.length == 0) return false;

        int rows = matrix.length;
        int columns = matrix[0].length;

        int low = 0;
        int high = rows * columns;

        while(low < high) {
            int mid = (low+high)/2;

            if(matrix[mid/columns][mid%columns] == target) {
                return true;
            } else if (matrix[mid/columns][mid%columns] < target) {
                low = mid+1;
            } else {
                high = mid;
            }
        }
        return false;
    }
}