Search a 2D Matrix

Write an efficient algorithm that searches for a value in an mx 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

Consider the following matrix:

[
    [1, 3, 5, 7],
    [10, 11, 16, 20],
    [23, 30, 34, 50]
]

Given target = 3, return true.

来源： http://www.lintcode.com/en/problem/search-a-2d-matrix/#

分析

首先想到的是将二维坐标转换为一维

public class Solution {
    /**
     * @param matrix, a list of lists of integers
     * @param target, an integer
     * @return a boolean, indicate whether matrix contains target
     */
    public boolean searchMatrix(int[][] matrix, int target) {
        // write your code here
        if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return false;
        int row = matrix.length;
        int col = matrix[0].length;
         
        int left = 0, right = row * col - 1;
        while(left < right){
            int mid = left + (right - left) / 2;
            int i = mid / col;
            int j = mid % col;
            if(matrix[i][j] < target){
                left = mid + 1;
            }
            else{
                right = mid;
            }
        }
        if(matrix[left / col][left % col] == target)
            return true;
        else
            return false;
    }
}

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