DAY 12
0

# JavaScript 解答

``````var longestPalindrome = function (s) {
var a = new Date();
var n = s.length;
var res = '';
var dp = [];
while (dp.push(new Array(n).fill(-1)) < n);
// console.log(dp);

for (var i = n - 1; i >= 0; i--) {
for (var j = i; j < n; j++) {
dp[i][j] = s[i] === s[j] && ((j - i < 3) || dp[i + 1][j - 1]);
if (dp[i][j] === undefined) {
console.log(i, j, s[i], s[j], dp[i + 1][j - 1])
}
if (dp[i][j]) {
var tmp = s.substring(i, j + 1);
if (tmp.length > res.length) res = tmp;
}

}
}
// console.log(dp);
console.log(new Date() - a);

return res;
};
``````

# Ruby 解答

``````def expand(s, center)
li, ri = center.floor, center.ceil
if li == ri
li -= 1
ri += 1
end
left_space = li
right_space = s.length - ri - 1
max_space = [left_space, right_space].min
most_left = li - max_space
while li >= most_left do
if s[li] == s[ri]
li -= 1
ri += 1
else
break
end
end
[ri - li - 1, li + 1, ri - 1]
end

def longest_palindrome(s)
i = 0
max_si, max_ei, max_len = nil, nil, 0
while i <= s.length - 1 do
len, si, ei = expand(s, i)
if max_len < len
max_si, max_ei, max_len = si, ei, len
end
i += 0.5
end
s[max_si..max_ei]
end
``````

30天刷題大挑戰16