[LeetCode] 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]
]

Given target =

3

, return

true

.

编程思想：从矩阵的右上角的元素开始与目标元素比较大小，矩阵右上角元素，比目标元素大的，删除矩阵右上角元素所在列，否则删除所在行，直到找到目标元素或者删除所有行列。

class Solution {
public:
bool searchMatrix(vector<vector<int> > &matrix, int target) {
if(matrix.empty())
return false;

int rows = matrix.size();
int columns = matrix[0].size();

int row = 0,column = columns-1;
while(row<rows && column>=0){
if(matrix[row][column]==target)
return true;
else if(matrix[row][column]>target)
column--;
else
row++;
}//end while
return false;
}
};