[LC] 74. Search a 2D Matrix

Posted 2021-03-23 xuanlu

Write 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 from left to right.
• The first integer of each row is greater than the last integer of the previous row.

Example 1:

Input:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 3
Output: true

Example 2:

Input:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 13
Output: false

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return false;
        }
        int row = matrix.length, col = matrix[0].length;
        int start = 0, end = row * col - 1;
        while (start <= end) {
            int mid = start + (end - start) / 2;
            int curRow = mid / col;
            int curCol = mid % col;
            if (matrix[curRow][curCol] == target) {
                return true;
            } else if (matrix[curRow][curCol] < target) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
        }
        return false;
    }
}