Leftmost Column with at Least a One

(This problem is an interactive problem.)

A binary matrix means that all elements are 0 or 1. For each individual row of the matrix, this row is sorted in non-decreasing order.

Given a row-sorted binary matrix binaryMatrix, return leftmost column index(0-indexed) with at least a 1 in it. If such index doesn't exist, return -1.

You can't access the Binary Matrix directly.  You may only access the matrix using a BinaryMatrix interface:

• BinaryMatrix.get(row, col) returns the element of the matrix at index (row, col) (0-indexed).
• BinaryMatrix.dimensions() returns a list of 2 elements [rows, cols], which means the matrix is rows * cols.

Submissions making more than 1000 calls to BinaryMatrix.get will be judged Wrong Answer.  Also, any solutions that attempt to circumvent the judge will result in disqualification.

For custom testing purposes you're given the binary matrix mat as input in the following four examples. You will not have access the binary matrix directly.

Example 1:

Input: mat = [[0,0],[1,1]]
Output: 0

Example 2:

Input: mat = [[0,0],[0,1]]
Output: 1

Example 3:

Input: mat = [[0,0],[0,0]]
Output: -1

Example 4:

Input: mat = [[0,0,0,1],[0,0,1,1],[0,1,1,1]]
Output: 1

思路：這題跟 search 2d matrix 一樣。遇見0，沒必要往左走了，因爲左邊全是0，遇見1了沒必要往下走，因爲我們是找最左邊的點；

 

/**
 * // This is the BinaryMatrix's API interface.
 * // You should not implement it, or speculate about its implementation
 * interface BinaryMatrix {
 *     public int get(int row, int col) {}
 *     public List<Integer> dimensions {}
 * };
 */

class Solution {
    public int leftMostColumnWithOne(BinaryMatrix binaryMatrix) {
        List<Integer> dimension = binaryMatrix.dimensions();
        int n = dimension.get(0);
        int m = dimension.get(1);
        int leftmost = -1;
        int i = 0; int j = m - 1;
        while(i < n && j >= 0) {
            if(binaryMatrix.get(i, j) == 0) {
                i++;
            } else {
                // binaryMatrix.get(i, j) == 1
                leftmost = j;
                j--;
            }
        }
        return leftmost;
    }
}