Leetcode: 74. Search a 2D Matrix

Description

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.

Example

Consider the following matrix:

[
    [1,   3,  5,  7],
    [10, 11, 16, 20],
     [23, 30, 34, 50]
]

Given target = 3, return true.

思路

• 从左下角或右上角开始找，大了就往上(下)，小了就往右(左)

代码

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