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.

分析

首先想到的是将二维坐标转换为一维
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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;
    }
}




posted @ 2017-02-14 10:22  copperface  阅读(207)  评论(0)  编辑  收藏  举报