python之正确的代码但错误的答案 :(

我正在解决 Project Euler Problem #18在 Python 中。

我已经成功解决了那里给出的示例问题，但未能解决主要问题。但是代码是一样的。

代码是:

matrix = [('75', '0'), 
    ('95', '64'), 
    ('17', '47', '82'), 
    ('18', '35', '87', '10'), 
    ('20', '04', '82', '47', '65'), 
    ('19', '01', '23', '75', '03', '34'), 
    ('88', '02', '77', '73', '07', '63', '67'), 
    ('99', '65', '04', '28', '06', '16', '70', '92'), 
    ('41', '41', '26', '56', '83', '40', '80', '70', '33'), 
    ('41', '48', '72', '33', '47', '32', '37', '16', '94', '29'), 
    ('53', '71', '44', '65', '25', '43', '91', '52', '97', '51', '14'), 
    ('70', '11', '33', '28', '77', '73', '17', '78', '39', '68', '17', '57'), 
    ('91', '71', '52', '38', '17', '14', '91', '43', '58', '50', '27', '29', '48'), 
    ('63', '66', '04', '68', '89', '53', '67', '30', '73', '16', '69', '87', '40', '31'), 
    ('04', '62', '98', '27', '23', '09', '70', '98', '73', '93', '38', '53', '60', '04', '23')] 
 
i = 0 
j = 0 
len = len(matrix ) 
sum = 0 
 
for i in range(0,len): 
 
    if matrix [i][j] > matrix [i][j + 1]: 
        print matrix [i][j] 
        sum = sum + int(matrix [i][j]) 
    else: 
        print matrix [i][j+1] 
        j = j + 1 
        sum = sum + int(matrix [i][j]) 
print sum 

谁能告诉我哪里错了？