74. Search a 2D Matrix

class Solution(object):
    def searchMatrix(self, matrix, target):
        # 思路:
        # 1.先获得矩阵的维度m行n列
        # 2. while循环的条件是 0<=x<m 和 0<=y<n
        # 从矩阵的左下角开始遍历,分三种情况:
        # 1)matrix[x][y] == target
        # 2)matrix[x][y] < target: 向右移动
        # 3)matrix[x][y] > target: 向上移动
        
        if not matrix or not matrix[0]:
            return False
        x, y = len(matrix) - 1, 0
        m, n = len(matrix), len(matrix[0])
        while m > x >= 0 and n > y >= 0:
            if matrix[x][y] == target:
                return True
            elif matrix[x][y] < target:
                y += 1
            else:
                x -= 1
        return False