[LeetCode 解题报告]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.

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