[leetcode] 240. Search a 2D Matrix II

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.

For 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.

解法一：

从左下角数字开始，--row都比他小，++col都比他大。

class Solution {public:    bool searchMatrix(vector<vector<int>>& matrix, int target) {        if(matrix.empty()||matrix[0].empty()) return false;        if(target < matrix[0][0] || target > matrix.back().back()) return false;                int row = matrix.size()-1;        int col = 0;        while(1){            if(matrix[row][col]<target) ++col;            else if (matrix[row][col]>target) --row;            else return true;                        if(row<0 || col>=matrix[0].size()) break;        }        return false;                            }};