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.

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.

 

有序矩阵查找

 

C++:

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        int n = matrix.size() ;
        if (n == 0)
            return false ;
        int m = matrix[0].size() ;
        int i = 0 ;
        int j = m-1 ;
        while(i < n && j >= 0){
            if (matrix[i][j] == target){
                return true ;
            }else if (matrix[i][j] > target){
                j-- ;
            }else{
                i++ ;
            }
        }
        return false ;
    }
};