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additive-number.cpp
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additive-number.cpp
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// Time: O(n^3)
// Space: O(n)
class Solution {
public:
bool isAdditiveNumber(string num) {
for (int i = 1; i < num.length(); ++i) {
for (int j = i + 1; j < num.length(); ++j) {
string s1 = num.substr(0, i), s2 = num.substr(i, j - i);
if ((s1.length() > 1 && s1[0] == '0') ||
(s2.length() > 1 && s2[0] == '0')) {
continue;
}
string next = add(s1, s2);
string cur = s1 + s2 + next;
while (cur.length() < num.length()) {
s1 = s2;
s2 = next;
next = add(s1, s2);
cur += next;
}
if (cur == num) {
return true;
}
}
}
return false;
}
private:
string add(const string& m, const string& n) {
string res;
int res_length = max(m.length(), n.length()) ;
int carry = 0;
for (int i = 0; i < res_length; ++i) {
int m_digit_i = i < m.length() ? m[m.length() - 1 - i] - '0' : 0;
int n_digit_i = i < n.length() ? n[n.length() - 1 - i] - '0' : 0;
int sum = carry + m_digit_i + n_digit_i;
carry = sum / 10;
sum %= 10;
res.push_back('0' + sum);
}
if (carry) {
res.push_back('0' + carry);
}
reverse(res.begin(), res.end());
return res;
}
};