leetcode-month3-week10

Two Sum II Input array is sorted

package ygy.test.week10;import java.util.HashMap;import java.util.Map;/** * Created by guoyao on 2017/11/4. */public class TwoSumIIInputarrayissorted {    public int[] twoSum(int[] numbers, int target) {        if(numbers == null || numbers.length == 0 ) return  null ;        Map<Integer, Integer> map=new HashMap<>();        for(int i = 0 ; i < numbers.length ; i ++) {            int remain = target - numbers[i] ;            if (map.containsKey(remain)) {                return new int[]{map.get(remain)+1,i+1};            }            map.put(numbers[i], i);        }        return null ;    }    //leetcode answer    public int[] twoSum_1(int[] numbers, int target) {        int l = 0, r = numbers.length - 1;        while (numbers[l] + numbers[r] != target) {            if (numbers[l] + numbers[r] > target) r--;            else l++;        }        return new int[]{l + 1, r + 1};    }    //leetcode answer    public int[] twoSum_2(int[] num, int target) {        int[] indice = new int[2];        if (num == null || num.length < 2) return indice;        int left = 0, right = num.length - 1;        while (left < right) {            int v = num[left] + num[right];            if (v == target) {                indice[0] = left + 1;                indice[1] = right + 1;                break;            } else if (v > target) {                right --;            } else {                left ++;            }        }        return indice;    }}

Min Stack

package ygy.test.week10;import java.util.Stack;/** * Created by guoyao on 2017/11/3. */public class MinStack {    Integer min = Integer.MAX_VALUE ;    Stack<Integer> stack=new Stack<>();    /** initialize your data structure here. */    public MinStack() {    }    public void push(int x) {        if (x <= min) {            stack.push(min);            min = x ;        }        stack.push(x);    }    public void pop() {        if(stack.pop().equals(min))            min=stack.pop();    }    public int top() {        return stack.peek() ;    }    public int getMin() {        return  min ;    }    public static void main(String[] args) {        MinStack minStack=new MinStack();        minStack.push(512);        minStack.push(-1024);        minStack.push(-1024);        minStack.push(512);        minStack.pop();        //System.out.println(minStack.top());        System.out.println(minStack.getMin());        minStack.pop();        //System.out.println(minStack.top());        System.out.println(minStack.getMin());        minStack.pop();        System.out.println(minStack.getMin());    }}/** * Your MinStack object will be instantiated and called as such: * MinStack obj = new MinStack(); * obj.push(x); * obj.pop(); * int param_3 = obj.top(); * int param_4 = obj.getMin(); */

Intersection of Two Linked Lists

package ygy.test.week10;/** * Created by guoyao on 2017/11/3. */public class IntersectionofTwoLinkedLists {    public static void main(String[] agrs) {    }    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {        ListNode reverseA=reverse(headA);        ListNode reverseB=reverse(headB);        ListNode temp = null ;        while (reverseA != null && reverseB != null) {            if (reverseA == reverseB) {                temp = reverseA ;                reverseA =reverseA.next;                reverseB = reverseB.next ;                continue;            }        }        return reverse(temp);    }    public  ListNode reverse(ListNode head) {        ListNode cacheNode = null ;        while (head != null) {            ListNode temp = head.next ;            head.next = cacheNode ;            cacheNode = head ;            head = temp;        }        return cacheNode;    }    //leetcode answer    public ListNode getIntersectionNode_1(ListNode headA, ListNode headB) {        //boundary check        if(headA == null || headB == null) return null;        ListNode a = headA;        ListNode b = headB;        //if a & b have different len, then we will stop the loop after second iteration        while( a != b){            //for the end of first iteration, we just reset the pointer to the head of another linkedlist            a = a == null? headB : a.next;            b = b == null? headA : b.next;        }        return a;    }    //leetcode answer    public ListNode getIntersectionNode_2(ListNode headA, ListNode headB) {        int lenA = length(headA), lenB = length(headB);        // move headA and headB to the same start point        while (lenA > lenB) {            headA = headA.next;            lenA--;        }        while (lenA < lenB) {            headB = headB.next;            lenB--;        }        // find the intersection until end        while (headA != headB) {            headA = headA.next;            headB = headB.next;        }        return headA;    }    private int length(ListNode node) {        int length = 0;        while (node != null) {            node = node.next;            length++;        }        return length;    }}class ListNode {    int val;    ListNode next;    ListNode(int x) {        val=x;        next=null;    }}/** * Definition for singly-linked list. */

Excel Sheet Column Title

package ygy.test.week10;/** * Created by guoyao on 2017/11/5. */public class ExcelSheetColumnTitle {    public static void main(String[] agrs) {        System.out.println(convertToTitle(30));    }    public  static  String convertToTitle(int n) {        StringBuilder result = new StringBuilder();        while(n>0){            n--;            result.insert(0, (char)('A' + n % 26));            n /= 26;        }        return result.toString();    }}