recursion and digits

Author: zhongn2

GenerateParenthesis.cpp

@@ -0,0 +1,24 @@
+// this is easy to think of recursion
+// how we can do recursion??
+// think about inner and outer part
+// 1 and 2 consist of 3
+// n = 1 ()
+// n = 2 ()(), (())
+// n = 3 ()()(), (())(),()(()), ((())), (()())
+
+
+class Solution {
+public:
+    vector<string> generateParenthesis(int n) {
+        vector<string> result;
+        if(n == 0) return vector<string> (1, "");
+        if(n == 1) return vector<string> (1, "()");
+        for(int i = 0; i < n; i++){
+            for(auto inner : generateParenthesis(i))
+                for(auto outer : generateParenthesis( n - 1 - i))
+                    result.push_back("(" + inner + ")" + outer);
+        }
+        return result;
+        
+    }
+};

PlusOne.cpp

@@ -0,0 +1,47 @@
+class Solution {
+public:
+    vector<int> plusOne(vector<int> &digits) {
+        add(digits, 1);
+        return digits;
+    }
+    void add(vector<int> &digits, int d){
+        int c = d;
+        for(auto it = digits.rbegin(); it != digits.rend(); it++){
+            *it += c;
+             c = *it / 10;
+             *it %= 10;
+        }
+        if(c > 0) digits.insert(digits.begin(), 1);
+    }
+};
+
+
+// method2
+// 12 + 1 simeple one
+// 19 + 1 carry = 1
+// 9 + 1 digit number needs change
+
+class Solution {
+public:
+    vector<int> plusOne(vector<int> &digits) {
+        int carry = 1;
+        int n = digits.size();
+        
+        for(int i = n - 1; i >= 0; i--){
+            digits[i] += carry;
+            if(digits[i] >= 10){
+                digits[i] %= 10;
+                carry = 1;
+            }else{
+                carry = 0;
+                break;
+            }
+        }
+        if(carry == 1){
+            digits.insert(digits.begin(), 1);
+        }
+        
+        return digits;
+        
+    }
+};