240. Search a 2D Matrix II.cpp

/*
Problem 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 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.
*/

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