ericzhangdl · ericzhangdl · Mar 30, 2019 · Mar 30, 2019 · Mar 30, 2019 · Mar 31, 2019
diff --git a/.gitignore b/.gitignore
@@ -1,2 +1,3 @@
 .idea
 algorithms-java/out
+*.class
diff --git a/README.md b/README.md
diff --git a/algorithms/cpp/3Sum/3Sum.cpp b/algorithms/cpp/3Sum/3Sum.cpp
@@ -26,11 +26,12 @@
 #include <vector>
 #include <set>
 #include <algorithm>
+
 using namespace std;
 
 
 /*
- *   Simlar like "Two Number" problem, we can have the simlar solution.
+ *   Similar like "Two Number" problem, we can have the simlar solution.
  *
  *   Suppose the input array is S[0..n-1], 3SUM can be solved in O(n^2) time on average by 
  *   inserting each number S[i] into a hash table, and then for each index i and j,  
@@ -47,6 +48,7 @@ using namespace std;
 vector<vector<int> > threeSum(vector<int> &num) {
 
     vector< vector<int> > result;
+    if(num.size() == 0 || num.size() == 1 || num.size() == 2) return result;
 
     //sort the array, this is the key
     sort(num.begin(), num.end());
@@ -55,14 +57,14 @@ vector<vector<int> > threeSum(vector<int> &num) {
 
     for (int i=0; i<n-2; i++) {
         //skip the duplication
-        if (i>0 && num[i-1]==num[i]) continue;
+        if (i > 0 && num[i - 1] == num[i]) continue;
         int a = num[i];
-        int low = i+1;
-        int high = n-1;
-        while ( low < high ) {
+        int low = i + 1;
+        int high = n - 1;
+        while (low < high) {
             int b = num[low];
             int c = num[high];
-            if (a+b+c == 0) {
+            if (a + b + c == 0) {
                 //got the soultion
                 vector<int> v;
                 v.push_back(a);
@@ -71,17 +73,17 @@ vector<vector<int> > threeSum(vector<int> &num) {
                 result.push_back(v);
                 // Continue search for all triplet combinations summing to zero.
                 //skip the duplication
-                while(low<n && num[low]==num[low+1]) low++; 
-                while(high>0 && num[high]==num[high-1]) high--; 
+                while(low < n - 1 && num[low] == num[low + 1]) low++; 
+                while(high > 0 && num[high] == num[high - 1]) high--; 
                 low++;
                 high--;
             } else if (a+b+c > 0) {
                 //skip the duplication
-                while(high>0 && num[high]==num[high-1]) high--;
+                while(high > 0 && num[high] == num[high - 1]) high--;
                 high--;
-            } else{
+            } else {
                 //skip the duplication
-                while(low<n && num[low]==num[low+1]) low++;
+                while(low < n - 1 && num[low] == num[low + 1]) low++;
                 low++;
             } 
         }
@@ -97,21 +99,21 @@ int sum(vector<int>& v);
 vector<vector<int> > threeSum2(vector<int> &num) {
     vector< vector<int> > result;
     vector< vector<int> > r = combination(num, 3);
-    for (int i=0; i<r.size(); i++){
-        if (isSumZero(r[i])){
+    for (int i = 0; i < r.size(); i++) {
+        if (isSumZero(r[i])) {
             result.push_back(r[i]);
         }
     }
     return result;
 }
 
-bool isSumZero(vector<int>& v){
-    return sum(v)==0;
+bool isSumZero(vector < int>& v) {
+    return sum(v) == 0;
 }
 
-int sum(vector<int>& v){
-    int s=0;
-    for(int i=0; i<v.size(); i++){
+int sum(vector<int>& v) {
+    int s = 0;
+    for(int i = 0; i < v.size(); i++) {
         s += v[i];
     }
     return s;
@@ -122,39 +124,39 @@ vector<vector<int> > combination(vector<int> &v, int k) {
     vector<vector<int> > result;
     vector<int> d;
     int n = v.size();
-    for (int i=0; i<n; i++){
-        d.push_back( (i<k) ? 1 : 0 );
+    for (int i = 0; i < n; i++) {
+        d.push_back( (i < k) ? 1 : 0 );
     }
 
     //1) from the left, find the [1,0] pattern, change it to [0,1]
     //2) move all of the 1 before the pattern to the most left side
     //3) check all of 1 move to the right
-    while(1){
+    while(1) {
         vector<int> tmp;
-        for(int x=0; x<n; x++){
+        for(int x = 0; x < n; x++) {
             if (d[x]) tmp.push_back(v[x]);
         }
         sort(tmp.begin(), tmp.end());
         result.push_back(tmp);
         //step 1), find [1,0] pattern
         int i;
         bool found = false;
-        int ones =0;
-        for(i=0; i<n-1; i++){
+        int ones = 0;
+        for(i = 0; i < n - 1; i++) {
 
-            if (d[i]==1 && d[i+1]==0){
-                d[i]=0; d[i+1]=1;
+            if (d[i] == 1 && d[i + 1] == 0) {
+                d[i] = 0; d[i + 1] = 1;
                 found = true;
                 //step 2) move all of right 1 to the most left side
-                for (int j=0; j<i; j++){
-                    d[j]=( ones > 0 ) ? 1 : 0;
+                for (int j = 0; j < i; j++) {
+                    d[j] = ( ones > 0 ) ? 1 : 0;
                     ones--;
                 }
                 break;
             }
-            if (d[i]==1) ones++;
+            if (d[i] == 1) ones++;
         }
-        if (!found){
+        if (!found) {
             break;
         }
 
@@ -165,9 +167,9 @@ vector<vector<int> > combination(vector<int> &v, int k) {
 
 void printMatrix(vector<vector<int> > &matrix)
 {
-    for(int i=0; i<matrix.size(); i++){
+    for(int i = 0; i < matrix.size(); i++) {
         printf("{");
-        for(int j=0; j< matrix[i].size(); j++) {
+        for(int j = 0; j < matrix[i].size(); j++) {
             printf("%3d ", matrix[i][j]) ;
         }
         printf("}\n");
@@ -178,9 +180,9 @@ void printMatrix(vector<vector<int> > &matrix)
 
 int main()
 {
-    //int a[] = {-1, 0, 1, 2, -1, 1, -4};
-    int a[] = {-1, 1, 1, 1, -1, -1, 0,0,0};
-    vector<int> n(a, a+sizeof(a)/sizeof(int));
+    //int a[] = { -1, 0, 1, 2, -1, 1, -4 };
+    int a[] = { -1, 1, 1, 1, -1, -1, 0,0,0 };
+    vector<int> n(a, a + sizeof(a)/sizeof(int));
     vector< vector<int> > result = threeSum(n);
     printMatrix(result);    
     return 0;

diff --git a/algorithms/cpp/3SumClosest/3SumClosest.cpp b/algorithms/cpp/3SumClosest/3SumClosest.cpp
@@ -21,6 +21,7 @@
 #include <vector>
 #include <set>
 #include <algorithm>
+
 using namespace std;
 
 #define INT_MAX 2147483647
@@ -53,34 +54,33 @@ int threeSumClosest(vector<int> &num, int target) {
 
     for (int i=0; i<n-2; i++) {
         //skip the duplication
-        if (i>0 && num[i-1]==num[i]) continue;
+        if (i > 0 && num[i - 1] == num[i]) continue;
         int a = num[i];
-        int low = i+1;
-        int high = n-1;
+        int low = i + 1;
+        int high = n - 1;
         //convert the 3sum to 2sum problem
-        while ( low < high ) {
+        while (low < high) {
             int b = num[low];
             int c = num[high];
-            int sum = a+b+c;
+            int sum = a + b + c;
             if (sum - target == 0) {
                 //got the final soultion
                 return target;
             } else {
-
                 //tracking the minmal distance
-                if (abs(sum-target) < distance ) {
+                if (abs(sum - target) < distance ) {
                     distance = abs(sum - target);
                     result = sum;
                 }
 
-                if (sum -target> 0) {
+                if (sum - target > 0) {
                     //skip the duplication
-                    while(high>0 && num[high]==num[high-1]) high--;
+                    while(high > 0 && num[high] == num[high - 1]) high--;
                     //move the `high` pointer
                     high--;
                 } else {
                     //skip the duplication
-                    while(low<n && num[low]==num[low+1]) low++;
+                    while(low < n && num[low] == num[low + 1]) low++;
                     //move the `low` pointer
                     low++;
                 }
@@ -96,8 +96,8 @@ int threeSumClosest(vector<int> &num, int target) {
 
 int main()
 {
-    int a[] = {-1, 2, 1, -4};
-    vector<int> n(a, a+sizeof(a)/sizeof(int));
+    int a[] = { -1, 2, 1, -4 };
+    vector<int> n(a, a + sizeof(a)/sizeof(int));
     int target = 1;
     cout << threeSumClosest(n, target) << endl;
     return 0;

diff --git a/algorithms/cpp/4Sum/4Sum.cpp b/algorithms/cpp/4Sum/4Sum.cpp
@@ -25,6 +25,7 @@
 #include <iostream>
 #include <vector>
 #include <algorithm>
+
 using namespace std;
 
 vector<vector<int> > threeSum(vector<int> num, int target); 
@@ -36,15 +37,15 @@ vector<vector<int> > threeSum(vector<int> num, int target);
 
 vector<vector<int> > fourSum(vector<int> &num, int target) {
     vector< vector<int> > result;
-    if (num.size()<4) return result;
+    if (num.size() < 4) return result;
     sort( num.begin(), num.end() );
-    
-    for(int i=0; i<num.size()-3; i++) {
+
+    for(int i = 0; i < num.size() - 3; i++) {
         //skip the duplication
-        if (i>0 && num[i-1]==num[i]) continue;
+        if (i > 0 && num[i - 1] == num[i]) continue;
         vector<int> n(num.begin()+i+1, num.end());
         vector<vector<int> > ret = threeSum(n, target-num[i]);
-        for(int j=0; j<ret.size(); j++){
+        for(int j = 0; j < ret.size(); j++) {
             ret[j].insert(ret[j].begin(), num[i]);
             result.push_back(ret[j]);
         }
@@ -61,16 +62,16 @@ vector<vector<int> > threeSum(vector<int> num, int target) {
 
     int n = num.size();
 
-    for (int i=0; i<n-2; i++) {
+    for (int i = 0; i < n - 2; i++) {
         //skip the duplication
-        if (i>0 && num[i-1]==num[i]) continue;
+        if (i > 0 && num[i - 1] == num[i]) continue;
         int a = num[i];
-        int low = i+1;
-        int high = n-1;
-        while ( low < high ) {
+        int low = i + 1;
+        int high = n - 1;
+        while (low < high) {
             int b = num[low];
             int c = num[high];
-            if (a+b+c == target) {
+            if (a + b + c == target) {
                 //got the soultion
                 vector<int> v;
                 v.push_back(a);
@@ -79,17 +80,17 @@ vector<vector<int> > threeSum(vector<int> num, int target) {
                 result.push_back(v);
                 // Continue search for all triplet combinations summing to zero.
                 //skip the duplication
-                while(low<n && num[low]==num[low+1]) low++;
-                while(high>0 && num[high]==num[high-1]) high--;
+                while(low < n && num[low] == num[low + 1]) low++;
+                while(high > 0 && num[high] == num[high - 1]) high--;
                 low++;
                 high--;
-            } else if (a+b+c > target) {
+            } else if (a + b + c > target) {
                 //skip the duplication
-                while(high>0 && num[high]==num[high-1]) high--;
+                while(high > 0 && num[high] == num[high - 1]) high--;
                 high--;
-            } else{
+            } else {
                 //skip the duplication
-                while(low<n && num[low]==num[low+1]) low++;
+                while(low < n && num[low] == num[low + 1]) low++;
                 low++;
             }
         }
@@ -100,9 +101,9 @@ vector<vector<int> > threeSum(vector<int> num, int target) {
 
 int printMatrix(vector< vector<int> > &vv)
 {
-    for(int i=0; i<vv.size(); i++) {
+    for(int i = 0; i < vv.size(); i++) {
         cout << "[";
-        for(int j=0; j<vv[i].size(); j++) {
+        for(int j = 0; j < vv[i].size(); j++) {
             cout << " " << vv[i][j];
         }
         cout << "]" << endl;;
@@ -112,14 +113,14 @@ int printMatrix(vector< vector<int> > &vv)
 
 int main()
 {
-    int a[] = {1,0,-1,0,-2,2};
+    int a[] = { 1, 0, -1, 0, -2, 2 };
     vector<int> n(a, a+6);
     int t = 0;
     vector< vector<int> > v = fourSum(n, t);
     printMatrix(v);
 
     n.clear();
-    int b[] = {-1,-5,-5,-3,2,5,0,4};
+    int b[] = { -1, -5, -5, -3, 2, 5, 0, 4 };
     n.insert(n.begin(), b, b+8);
     t = -7;
     v = fourSum(n, t);