lintcode做题总结, Sept 18

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1. Number of 1 Bits My Submissions Question Solution

这道题本来很简单的，但是在测试中参数int的值会越界，我也不知道是怎么穿进去的

public class Solution {    // you need to treat n as an unsigned value    public int hammingWeight(int n) {        int count = 0;        for(int i=1; i<33; i++){            if(((n>>i) & (1)) != 0){                count++;            }        }        return count;    }}

2. House Robber 这道题用的是一维DP

public class Solution {    public int rob(int[] num) {        if(num==null || num.length==0)            return 0;         int n = num.length;             int[] dp = new int[n+1];        dp[0]=0;        dp[1]=num[0];             for (int i=2; i<n+1; i++){           dp[i] = Math.max(dp[i-1], dp[i-2]+num[i-1]);        }             return dp[n];    }}

3. Happy Number 这道题好没意思，就是简单的计算

public class Solution {    public boolean isHappy(int n) {        HashSet<Integer> set = new HashSet<Integer>();        while(!set.contains(n)){            set.add(n);            n = sum(getDigits(n));            if (n == 1)                return true;        }        return false;    }    public int sum(int[] arr){        int sum = 0;        for(int i: arr){            sum = sum + i*i;        }        return sum;    }     public int[] getDigits(int n){        String s = String.valueOf(n);        int[] result = new int[s.length()];        int i=0;        while(n>0){            int m = n%10;            result[i++] = m;            n = n/10;        }        return result;    }}

4. Remove Linked List Elements 链表删除元素

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public ListNode removeElements(ListNode head, int val) {        ListNode helper = new ListNode(0);        helper.next = head;        ListNode p = helper;             while(p.next != null){            if(p.next.val == val){                ListNode next = p.next;                p.next = next.next;             }else{                p = p.next;            }        }             return helper.next;    }}

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