Search a 2D Matrix

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.

 

For example,

Consider the following matrix:

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

  这道题还是比较简单的，在一个二维数组查找一个指定元素。可以直接遍历这个数组，不过已经排好序，可以先查找在哪一行，然后在对该行进行二分查找

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        boolean foundIndex = false;
        int index = 0;
        for(int i = 0; i < matrix.length - 1; i++){
            if(matrix[i][0] <= target && matrix[i + 1][0] > target){
                foundIndex = true;
                index = i;
                break;
            }
        }//for
        if(foundIndex){
            return searchByBS(matrix[index], target);
        }
        else
            return searchByBS(matrix[matrix.length - 1], target);
    }
    
    /**
     * 对数组进行二分查找
     * @param num
     * @return
     */
    public boolean searchByBS(int num[],int  target){
        int low = 0;
        int high = num.length - 1;
        int middle;
        while(low <= high){
            middle = (low + high) / 2;
            if(num[middle] == target)
                return true;
            else if(num[middle] > target){
                high = middle - 1;
            }else{
                low = middle + 1;
            }//else if
        }//while
        return false;
    }
}