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| class Solution {
public boolean isAdditiveNumber(String num) {
for (int j = 1; j < num.length() - 1; j++) {
String firstNum = num.substring(0, j);
for (int k = j + 1; k < num.length(); k++) {
String secondNum = num.substring(j, k);
if (dfs(num, k, firstNum, secondNum, true)) {
return true;
}
}
}
return false;
}
private boolean dfs(String num, int startIndex, String firstNum, String secondNum, boolean firstMatch) {
if (firstNum.length() > 1 && firstNum.startsWith("0")) {
return false;
}
if (secondNum.length() > 1 && secondNum.startsWith("0")) {
return false;
}
if (startIndex == num.length()) {
return !firstMatch;
}
String exceptedSum = add(firstNum, secondNum);
if (startIndex + exceptedSum.length() > num.length() || !num.startsWith(exceptedSum, startIndex)) {
return false;
}
return dfs(num, startIndex + exceptedSum.length(), secondNum, exceptedSum, false);
}
private String add(String str1, String str2) {
StringBuilder sb = new StringBuilder();
int carry = 0;
int i = str1.length() - 1, j = str2.length() - 1;
while (i >= 0 || j >= 0) {
int x = i >= 0 ? str1.charAt(i) - '0' : 0;
int y = j >= 0 ? str2.charAt(j) - '0' : 0;
int sum = carry + x + y;
carry = sum / 10;
sb.append(sum % 10);
i--;
j--;
}
if (carry != 0) {
sb.append(carry);
}
return sb.reverse().toString();
}
}
|