240 Search in a 2D matrix II

Write an efficient algorithm that searches for a value in an mxn 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, returntrue.

Given target=20, returnfalse.

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

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

    int row = 0;
    int col = m - 1;

    while (row < n && col >= 0) {
        if (matrix[row][col] == target) {
            return true;
        } else if (matrix[row][col] > target) {
            col--;
        } else {
            row++;
        }
    }

    return false;
}

L38 Search a 2D Matrix II

Write an efficient algorithm that searches for a value in an m x n matrix, return the occurrence of it.

This matrix has the following properties:

• Integers in each row are sorted from left to right.

• Integers in each column are sorted from up to bottom.

• No duplicate integers in each row or column.

Example

Consider the following matrix:

[
  [1, 3, 5, 7],
  [2, 4, 7, 8],
  [3, 5, 9, 10]
]

Given target =3, return2.

Challenge

O(m+n) time and O(1) extra space

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

        int cnt = 0;
        int n = matrix.length;
        int m = matrix[0].length;
        int i = 0;
        int j = m - 1;
        while (i < n && j >= 0) {
            if (matrix[i][j] > target) {
                j--;
            } else if (matrix[i][j] < target) {
                i++;
            } else {
                cnt++;
                i++;
                j--;
            }
        }

        return cnt;
    }