240. Search a 2D Matrix II (二维矩阵二分)

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题目链接
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.

视频题解

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