CodingProblems/ExpressionAddOperation.java at master · PerrySong/CodingProblems · GitHub

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importjava.util.ArrayList;
importjava.util.List;
importjava.util.Stack;

publicclassExpressionAddOperation {
/**
 Given a string that contains only digits 0-9 and a target value, return all possibilities to add binary operators (not unary) +, -, or * between the digits so they evaluate to the target value.

 Example 1:

 Input: num = "123", target = 6
 Output: ["1+2+3", "1*2*3"]
 Example 2:

 Input: num = "232", target = 8
 Output: ["2*3+2", "2+3*2"]
 Example 3:

 Input: num = "105", target = 5
 Output: ["1*0+5","10-5"]
 Example 4:

 Input: num = "00", target = 0
 Output: ["0+0", "0-0", "0*0"]
 Example 5:

 Input: num = "3456237490", target = 9191
 Output: []
 */
publicList<String> addOperators(Stringnum, inttarget) {
List<String> res = newArrayList<>();
if (num == null || num.length() == 0) returnres;
// 1. partition the numbers
List<List<Long>> partitions = newArrayList<>();
partition(partitions, newArrayList<>(), num); // n!

// 2. try different operator
for (List<Long> numsList : partitions) { // m
List<String> formulars = newArrayList<>();
formFormulars(formulars, newStringBuilder(), numsList, 0); // O(3 ^ k)
for (Stringformular : formulars) {

if (result(formular) == (long)target) {
System.out.println(formular);
System.out.println(result(formular));
res.add(formular); // O(n)
 }
 }
 }
returnres;
 }

publicvoidpartition(List<List<Long>> res, List<Long> tmp, Stringnum) {
if (num.length() == 0) {
res.add(newArrayList<>(tmp));
return;
 }

for(inti = 1; i <= num.length(); i++) {
StringcurNUm = num.substring(0, i);
if (curNUm.charAt(0) == '0' && i > 1) continue;
tmp.add(Long.valueOf(curNUm));
partition(res, tmp, num.substring(i));
tmp.remove(tmp.size() - 1);
 }
 }

publicvoidformFormulars(List<String> res, StringBuildertmp, List<Long> numList, intstart) {
intoriSize = tmp.length();
tmp.append(numList.get(start));
if (start >= numList.size() - 1) {
res.add(tmp.toString());
tmp.delete(oriSize, tmp.length());
return;
 }
char[] ops = newchar[] {'+', '-', '*'};
for (charop : ops) {
tmp.append(op);
formFormulars(res, tmp, numList, start + 1);
tmp.deleteCharAt(tmp.length() - 1);
 }
tmp.delete(oriSize, tmp.length());
 }

publiclongresult(Stringformular) {
intres = 0;
char[] ops = getOps(formular);
String[] nums = formular.split("[^0-9]"); // Will generate an empty "" in the front
if (nums.length == 1) returnLong.valueOf(nums[0]);
Stack<Long> stack = newStack<>();
stack.push(Long.valueOf(nums[0]));
for (inti = 1; i < nums.length; i++) {
if (ops[i - 1]== '+') {
stack.push(Long.valueOf(nums[i]));
 } elseif (ops[i - 1]== '-') {
stack.push(-Long.valueOf(nums[i]));
 } elseif (ops[i - 1]== '*') {
stack.push(stack.pop() * Long.valueOf(nums[i]));
 }
 }

while (!stack.isEmpty()) {
res += stack.pop();
 }
returnres;
 }

publicchar[] getOps(Stringformular) {
intsize = 0;
for (charc : formular.toCharArray()) {
if (c == '+' || c == '-' || c == '*') {
size++;
 }
 }

char[] res = newchar[size];
inti = 0;
for (charc : formular.toCharArray()) {
if (c == '+' || c == '-' || c == '*') {
res[i++] = c;
 }
 }
returnres;
 }

publicstaticvoidmain(String[] args) {
ExpressionAddOperationa = newExpressionAddOperation();
// a.addOperators("3456237490",9191);
// a.addOperators("105", 5);
a.addOperators("2147483648",
 -2147483648);
// System.out.println(a.result("10-5"));
 }
}