sort methods and leetcode update

Author: zhongn2

AllKindofSort.cpp

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+#include <iostream>
+#include <iterator>
+#include <vector>
+#include <stdlib.h>
+#include <cstdlib>
+
+
+
+// selection srot
+void selectionSort(int unsort[], int n){
+	for(int i = 0; i < n; i ++){
+		int min = unsort[i];
+		int min_index = i;// record the position for swapping
+		for(int j = i; j < n; j++){
+			if( min > unsort[j]){
+				min = unsort[j];
+				min_index = j;
+			}
+		}
+		// exchange the two values of i and min_index
+		// in order to put the smallest number at front
+		if(min_index!= i){
+			int temp = unsort[i];
+			unsort[i] = unsort[min_index];
+			unsort[min_index] = temp;
+		}
+	}
+}
+
+// Time Complexity is O(n^2)
+pseudocode:
+for i= 0:n;
+	for j =i:n;
+	if (A[i] > A[j])
+		swap( A[i], A[j]);
+
+void BubbleSort(int unsort[], int n){
+	for(int i = 0; i < n; i ++){// outer looper
+		for( int j = 0; j < n-1-i; j ++){ // inner loop, the elements before
+			if( unsort[j] > unsort[j+1]){
+				// swap unsort[j] and unsort[j+1]
+				int temp = unsort[j];
+				unsort[j] = unsort[j+1];
+				unsort[j+1] = temp;
+			}
+		}
+	}
+}
+// to be continued 
+// merge sort //insertion sort // quick sort - in place ??
+
+void InsertionSort(int unsort[], int n){
+	for(int i = 1; i < n; i ++){ // outter loop is to keep checking each int
+		int value = unsort[i];
+		int j = i - 1;
+		while(j >= 0 && unsort[j] > value){ // compare each int with the formal ordered list and insert into appriproate position
+			unsort[j+1] = unsort[j];
+			j --; // j -- stands for iterator from right to left
+			unsort[j+1] = value;
+		}
+	}
+}
+
+
+
+// mergesort implemented here and make sure about the inputs
+// sounds like the input is stupid
+
+void merge(int unsorted[], int first, int mid, int last, int sorted[]){
+	 int i = first, j = mid, k = 0;
+	 while( i < mid && j < last){
+		 if(unsorted[i] < unsorted[j])
+			 sorted[k++] = unsorted[i++]; // sort[k] = unsorted[j]; k ++; j ++;
+		 else
+			 sorted[k++] = unsorted[j++];
+	 }
+	 while( i < mid)
+		 sorted[k++] = unsorted[i++];
+	 while( j < last)
+		 sorted[k++] = unsorted[j++];
+		 
+	 for(int m = 0; m < k; m++)
+		 unsorted[first + m] = sorted[m];
+}
+
+void Merge_Sort(int unsorted[], int first, int last, int sorted[]){
+	if( last > first +1){
+		int mid = (first + last) /2;
+		Merge_Sort(unsorted, first, mid, sorted);
+		Merge_Sort(unsorted, mid, last, sorted);
+		merge(unsorted, first,mid, last, sorted);
+	}
+}
+
+// find partition of the array
+int partition(int unsorted[], int low, int high){
+	int pivot = unsorted[low];
+	while( low < high){
+		while( (low < high) && (unsorted[high] > pivot)) high --;
+		unsorted[low] = unsorted[high];
+		while( (low < high) && ( unsorted[low] <= pivot)) low ++;
+		unsorted[high] = unsorted[low];
+	}
+	unsorted[low] = pivot;
+	return low;
+}
+
+
+void quick_sort(int unsorted[], int low, int high){
+	int p;
+	if( low < high){
+		p = partition(unsorted, low, high);
+		quick_sort(unsorted, low, p - 1);
+		quick_sort(unsorted, p + 1, high);
+	}
+}
+
+
+int main(){
+	int unsorted[6] = {5,6,3,9,7,8};
+	int sorted[6];
+	//selectionSort(unsorted,7);
+	//BubbleSort(unsorted, 7);
+	//InsertionSort(unsorted,7);
+	//Merge_Sort(unsorted,0, 6, sorted);
+	quick_sort(unsorted,0,5);
+	std::copy(unsorted, unsorted+6, std::ostream_iterator<int> (std::cout, " "));
+	std::cin.get();
+	return 0;
+}

Valid Palindrome.cpp

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+//we have two pointers, starts from begin and the other starts from end
+// pseudo code as following:
+// while( i < j){
+// if(!isalnum(S[i]) i ++; continue;
+// if(!isalnum(S[j]) j --; continue;
+
+class Solution {
+public:
+    bool isPalindrome(string s) {
+        if(s.size() == 0) return true;
+        int i = 0, j = s.size() - 1;
+        while( i < j){
+            if(!isalnum(s[i])){
+                i ++; continue;
+            }
+            if(!isalnum(s[j])){
+                j --; continue;
+            } // keep i and j at the same level
+            if(tolower(s[i]) != tolower(s[j]))
+                return false;
+            else{
+                i ++;
+                j --;
+            }
+        }
+        return true;
+    }
+};