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ExpressionAddOperators.java
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180 lines (170 loc) · 6.79 KB
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import java.util.*;
public class ExpressionAddOperators {
private static void backTrack(String num, int target, int start, long sum, long subSum, char prevSign,
StringBuilder sb, List<String> result) {
int prevSbLength = sb.length();
if (start >= num.length()) {
if (prevSign == '+' && (sum + subSum) == target) {
result.add(sb.toString());
}
return;
}
if (start > 0) {
sb.append(prevSign);
}
long curNum = 0;
for (int i = start; i < num.length(); ++i) {
curNum = 10 * curNum + (int)(num.charAt(i) - '0');
sb.append(num.charAt(i));
long tempSum = sum;
long tempSubSum = subSum;
switch (prevSign) {
case '+' : tempSum += tempSubSum;
tempSubSum = curNum;
break;
case '-' : tempSum += tempSubSum;
tempSubSum = -curNum;
break;
case '*' : tempSubSum *= curNum;
}
backTrack(num, target, i+1, tempSum, tempSubSum, '+', sb, result);
backTrack(num, target, i+1, tempSum, tempSubSum, '-', sb, result);
backTrack(num, target, i+1, tempSum, tempSubSum, '*', sb, result);
if (i == start && num.charAt(i) == '0') {
break;
}
}
sb.setLength(prevSbLength);
}
public List<String> addOperators0(String num, int target) {
List<String> result = new ArrayList<>();
backTrack(num, target, 0, 0, 0, '+', new StringBuilder(), result);
return result;
}
//Improved backtrack solution:
private static void backTrack(String num, long target, int start, long sum, long subSum,
StringBuilder sb, List<String> result) {
if (start >= num.length()) {
if ((sum + subSum) == target) {
result.add(sb.toString());
}
return;
}
long curNum = 0;
StringBuilder curSb = new StringBuilder();
int originalSbLength = sb.length();
for (int i = start; i < num.length(); ++i) {
curNum = 10 * curNum + (int)(num.charAt(i) - '0');
curSb.append(num.charAt(i));
if (start == 0) {
backTrack(num, target, i+1, sum + subSum, curNum, sb.append(curSb), result);
} else {
int signId = sb.length();
backTrack(num, target, i+1, sum + subSum, curNum, sb.append('+').append(curSb), result);
sb.setCharAt(signId, '-');
backTrack(num, target, i+1, sum + subSum, -curNum, sb, result);
sb.setCharAt(signId, '*');
backTrack(num, target, i+1, sum, subSum * curNum, sb, result);
}
sb.setLength(originalSbLength);
if (i == start && num.charAt(i) == '0') {
break;
}
}
}
//Slightly improved from above
private static void backTrack(String num, int target, int start, long sum, long subSum,
StringBuilder sb, List<String> result) {
if (start >= num.length() || sum > Integer.MAX_VALUE || sum < Integer.MIN_VALUE
|| subSum > Integer.MAX_VALUE) {
if ((sum + subSum) == target) {
result.add(sb.toString());
}
return;
}
long curNum = 0;
StringBuilder curSb = new StringBuilder();
int originalSbLength = sb.length();
for (int i = start; i < num.length(); ++i) {
curNum = 10 * curNum + (int)(num.charAt(i) - '0');
curSb.append(num.charAt(i));
if (start == 0) {
backTrack(num, target, i+1, sum + subSum, curNum, sb.append(curSb), result);
} else {
int signId = sb.length();
backTrack(num, target, i+1, sum + subSum, curNum, sb.append('+').append(curSb), result);
sb.setCharAt(signId, '-');
backTrack(num, target, i+1, sum + subSum, -curNum, sb, result);
sb.setCharAt(signId, '*');
backTrack(num, target, i+1, sum, subSum * curNum, sb, result);
}
sb.setLength(originalSbLength);
if (curNum == 0) {
break;
}
}
}
//Same logic as above, but use char[] instead of StringBuilder.
//Much faster on OJ.
private static void backTrack(String num, long target, int start, long sum, long subSum,
char[] exp, int expLen, List<String> result) {
if (start >= num.length()) {
if ((sum + subSum) == target) {
result.add(new String(exp, 0, expLen));
}
return;
}
long curNum = 0;
int expId = (start == 0) ? expLen : expLen + 1;
for (int i = start; i < num.length(); ++i) {
curNum = 10 * curNum + (int)(num.charAt(i) - '0');
exp[expId++] = num.charAt(i);
if (start == 0) {
backTrack(num, target, i+1, sum + subSum, curNum, exp, expId, result);
} else {
exp[expLen] = '+';
backTrack(num, target, i+1, sum + subSum, curNum, exp, expId, result);
exp[expLen] = '-';
backTrack(num, target, i+1, sum + subSum, -curNum, exp, expId, result);
exp[expLen] = '*';
backTrack(num, target, i+1, sum, subSum * curNum, exp, expId, result);
}
if (i == start && num.charAt(i) == '0') {
break;
}
}
}
public List<String> addOperators(String num, int target) {
List<String> result = new ArrayList<>();
backTrack(num, target, 0, 0, 0, new StringBuilder(), result);
return result;
}
private static boolean hasDuplicates(List<String> result) {
Set<String> uniqueStrs = new HashSet<>();
for (String str : result) {
if (uniqueStrs.contains(str)) {
System.out.println("Duplicate: " + str);
}
uniqueStrs.add(str);
}
System.out.println("Number of results = " + result.size());
return uniqueStrs.size() != result.size();
}
public static void main(String[] args) {
String[] tests = new String[] {
"1000000009"
};
int[] targets = new int[] {
9
};
ExpressionAddOperators solution = new ExpressionAddOperators();
for (int i = 0; i < tests.length; ++i) {
String test = tests[i];
int target = targets[i];
System.out.println(test + ", " + target);
List<String> result = solution.addOperators(test, target);
boolean foundDuplicates = hasDuplicates(result);
System.out.println("Found duplicate = " + foundDuplicates);
}
}
}