Search a 2D Matrix II

Description

Write an efficient algorithm that searches for a value in an m x n matrix, return the occurrence of it.

This matrix has the following properties:

• Integers in each row are sorted from left to right.
• Integers in each column are sorted from up to bottom.
• No duplicate integers in each row or column.

Example

Consider the following matrix:

[
  [1, 3, 5, 7],
  [2, 4, 7, 8],
  [3, 5, 9, 10]
]

Given target =3, return2.

Challenge

O(m+n) time and O(1) extra space

Related problems

Kth Smallest Sum In Two Sorted Arrays

Easy Search a 2D Matrix

Implementation

Link: http://lintcode.com/en/problem/search-a-2d-matrix-ii/

class Solution {
public:
    /**
     * @param matrix: A list of lists of integers
     * @param target: An integer you want to search in matrix
     * @return: An integer indicate the total occurrence of target in the given matrix
     */
    int searchMatrix(vector<vector<int> > &matrix, int target) {
        // write your code here
        if(matrix.size() == 0 || matrix[0].size() == 0) return 0;

        int m = matrix.size();
        int n = matrix[0].size();

        int i = m - 1;
        int j = 0;
        int ret = 0;

        while(1){
            if(matrix[i][j] == target){
                i--;
                j++;
                ++ret;
            }else if(matrix[i][j] < target){
                j++;
            }else{ // matrix[i][j] > target
                i--;
            }

            if(j == n) break;
            if(i < 0) break;
        }

        return ret;
    }
};