74.Search a 2D Matrix&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 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.

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.

两道题貌似没什么区别

对于每一行，先跟最后一列比元素比，如果target大，则去下一行找，如果相等，返回true，如果target小，则在这行向前找。

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