題目

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 in ascending from left to right.
• Integers in each column are sorted in ascending from top to bottom.

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, return true.

Given target = 20, return false.

解法

二維矩陣的解法，注意題目是在有序的前提下：

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix==null||matrix.length==0||matrix[0].length==0) return false;
        int row=0;
        int col=matrix[0].length-1;
        while(row<matrix.length&&col>=0){
            int curr=matrix[row][col];
            if(target==curr){
                return true;
            }
            else if(target>curr){
                row++;
            }
            else{
                col--;
            }  
        }
        return false;
    }
}