从右上角或左下角开始，类似二叉搜索树BST

/**
 * 从右上角或者左上角开始运算，这样才能保证两个方向一个是变大一个是变小
 * Runtime: 4 ms, faster than 100.00%
 * Memory Usage: 44.8 MB, less than 31.44%
 */
class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int i = 0, j = matrix[0].length - 1;
        while (i < matrix.length && j >= 0) {
            if (matrix[i][j] == target) {
                return true;
            }
            if (target > matrix[i][j]) {
                i++;
            } else {
                j--;
            }
        }
        return false;
    }
}