240. Search a 2D Matrix II

rite an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. For example,

Consider the following matrix:

[
  [1,   4,  7, 11, 15],
  [2,   5,  8, 12, 19],
  [3,   6,  9, 16, 22],
  [10, 13, 14, 17, 24],
  [18, 21, 23, 26, 30]
]

Given target = 5, return true.

Given target = 20, return false.

//O(m+n)
public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix.length == 0 || matrix[0].length == 0) return false;
        int m = matrix.length-1;
        int n = matrix[0].length-1;

        int x = 0;
        int y = n;

        while(x <= m && y >=0){
            if(matrix[x][y] == target) return true;
            else if(matrix[x][y] > target) y--;
            else x++;
        }
        return false;
    }
}

O(lgm + logn ) solution

Wrong thinking, you cannot do a binary search row-wise, and then a binary search on col-wise, THIS IS TOTAL WRONG THINKING. the correct one is divide the panel to 4 parts

Check this copy paste solution.

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return false;
        }

        int m = matrix.length;
        int n = matrix[0].length;

        return helper(matrix, 0, m - 1, 0, n - 1, target);
    }

    private boolean helper(int[][] matrix, int rowStart, int rowEnd, int colStart, int colEnd, int target) {
        if (rowStart > rowEnd || colStart > colEnd) {
            return false;
        }

        int rowMid = rowStart + (rowEnd - rowStart) / 2;
        int colMid = colStart + (colEnd - colStart) / 2;

        if (matrix[rowMid][colMid] == target) {
            return true;
        }

        if (matrix[rowMid][colMid] > target) {
            return helper(matrix, rowStart, rowMid - 1, colStart, colMid - 1, target) ||
                helper(matrix, rowMid, rowEnd, colStart, colMid - 1, target) ||
                helper(matrix, rowStart, rowMid - 1, colMid, colEnd, target);
        } else {
            return helper(matrix, rowMid + 1, rowEnd, colMid + 1, colEnd, target) ||
                helper(matrix, rowMid + 1, rowEnd, colStart, colMid, target) ||
                helper(matrix, rowStart, rowMid, colMid + 1, colEnd, target);
        }
    }
}