add subtract curry function implement dynamic chain

Author: rvguradiya

problems/general/add_subtract_curry.md

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+This problem was asked by **Squarespace**.
+
+Write a function, add_subtract, which alternately adds and subtracts curried arguments. Here are some sample operations:
+
+```java
+add_subtract(7) -> 7
+
+add_subtract(1)(2)(3) -> 1 + 2 - 3 -> 0
+
+add_subtract(-5)(10)(3)(9) -> -5 + 10 - 3 + 9 -> 11
+```

solutions/general/add_subtract_curry/approach1.js

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+function add_subtract(n) {
+  let acc = n;
+  let op = true;
+
+  return function inner(m) {
+    if (!m) {
+      return acc;
+    }
+    acc += op ? m : -m;
+    op = !op;
+    return inner;
+  };
+}
+
+console.log(add_subtract(7)()); // Output: 7
+console.log(add_subtract(1)(2)(3)()); // Output: 0
+console.log(add_subtract(-5)(10)(3)(9)()); // Output: 11

solutions/general/add_subtract_curry/approach1.py

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+def add_subtract(n):
+    acc = n
+    op = True
+    def inner(m=None):
+        nonlocal acc
+        nonlocal op
+        if m is None:
+            return acc
+        if op:
+            acc += m
+        else:
+            acc -= m
+        op = not op
+        return inner
+    return inner
+
+# Examples
+print(add_subtract(7)())          # Output: 7
+print(add_subtract(1)(2)(3)())    # Output: 0
+print(add_subtract(-5)(10)(3)(9)()) # Output: 11