剑指offer题目41-50

面试题41：和为S的连续正整数序列

import java.util.ArrayList;
public class Solution {
    public ArrayList<ArrayList<Integer> > FindContinuousSequence(int sum) {
       ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
       int start = 1;
       int end   = 2;
       int mid   = (1 + sum)/2;
       int curSum = start + end;
       while(start < mid){
            if(curSum == sum){
                ArrayList<Integer> list = makeList(start,end);
                res.add(list);              
            }
            while(curSum > sum && start < mid){
                curSum -= start;
                start++;
                if(curSum == sum){
                    ArrayList<Integer> list = makeList(start,end);
                    res.add(list);
                }
            }
            end ++;
            curSum += end;
       } 
       return res;
    }
    public ArrayList<Integer> makeList(int start , int end){
        ArrayList<Integer> list = new ArrayList<Integer>();
        for(int i=start;i<=end;i++){
            list.add(i);
        }
        return list;
    }
}

面试题41：递增序列中乘积最小的和为S的两个数

import java.util.ArrayList;
import java.util.HashMap;
public class Solution {
    public ArrayList<Integer> FindNumbersWithSum(int [] array,int sum) {       
        ArrayList<Integer> res = new ArrayList<Integer>();
        if(array == null && array.length <2 ) return res;
        int first = 0;
        int second = array.length-1;
        int len = array.length;
        int mul = Integer.MAX_VALUE;
        int retFirst = 0;
        int retSecond = 0 ;
        HashMap<Integer,Integer> map = new HashMap<Integer,Integer>();
        for(int i=0;i<array.length;i++){
            map.put(array[i],i);
        }
        while(first<second && first<len-1 && second<len){
            if(map.get(sum - array[first])!=null && map.get(sum - array[first])>first){
                second = map.get(sum - array[first]);
                int tmpMul = array[first] * array[second];
                if(tmpMul < mul){
                    mul = tmpMul;
                    retFirst = array[first];
                    retSecond = array[second];
                }
            }
            first++;
        }
        if(retFirst>0 && retSecond>0){
            res.add(retFirst);
            res.add(retSecond);
        }
        return res;
    }
}

面试题42：左旋转字符串

public class Solution {
    public String LeftRotateString(String str,int n) {
        if(str == null || n>str.length()) return "";
        char[] arr = str.toCharArray();
        reverse(arr,0,n-1);
        reverse(arr,n,arr.length-1);
        reverse(arr,0,arr.length-1);
        StringBuilder strBuilder = new StringBuilder();
        for(int i=0;i<arr.length;i++){
            strBuilder.append(arr[i]);
        }
        return strBuilder.toString();
    }
    public void reverse(char[] arr,int start,int end){
        while(start < end){
            char tmp = arr[end];
            arr[end--] = arr[start];
            arr[start++] = tmp;
        }
    }
}

面试题42：翻转单词序列

public class Solution {
    public String ReverseSentence(String str) {
        if (str == null || str.length() == 0 || str.trim().equals("")) {
            return str;
        }  
        char[] arr = str.toCharArray();
        reverse(arr,0,arr.length-1);
        int start = 0,end=0;
        for(int i=0;i<arr.length;i++){
            if(arr[i] != ' '){
                arr[end++] = arr[i];
            }else if(i>0 && arr[i-1] != ' '){
                reverse(arr,start,end-1);
                arr[end++] = ' ';
                start = end;
            }
        }
        reverse(arr,start,end-1);
        return new String(arr,0,end>0&&arr[end-1]==' ' ? end-1:end);
    }
    public void reverse(char[] arr,int start,int end){
        while(start < end){
            char tmp = arr[end];
            arr[end--] = arr[start];
            arr[start++] = tmp;
        }
    }
}

面试题44：扑克牌的顺子

import java.util.Arrays;
public class Solution {
    public boolean isContinuous(int [] numbers) {
        if(numbers.length==0) return false;
        if(numbers.length==1) return true;
        Arrays.sort(numbers);
        int i=0;
        int zeroCnt = 0;
        while(numbers[i] == 0){
            zeroCnt++;
            i++;
        }
        int notConCnt = 0;
        while(i<numbers.length){
            if(i>0 && numbers[i] == numbers[i-1]) return false;
            if(i>0 && numbers[i] != numbers[i-1] && numbers[i-1]!=0){
                notConCnt += (numbers[i] - numbers[i-1] - 1);
            }
            i++;
        }
        if(zeroCnt >= notConCnt || notConCnt == 0) return true;
        else return false;
    }
}

面试题45：约瑟夫环

public class Solution {
    public int LastRemaining_Solution(int n, int m) {
        if(n==0) return -1;
        int i=0,r=0;
        for(i=2;i<=n;i++){
            r = (r + m)%i;
        }
        return r;
    }
}

面试题46：不用循环和判断语句求从1到n的和

public class Solution {
    public int Sum_Solution(int n) {
        int res = n;
        boolean ans = (n>0) && ((res = Sum_Solution(n-1) + res)>0) ;
        return res;
    }
}

面试题47：不用加减乘除做加法

public class Solution {
    public int Add(int num1,int num2) {
        int sum ,carry;
        do{
            sum = num1 ^ num2;
            carry = (num1 & num2)<<1;
            num1 = sum;
            num2 = carry;
        }while(num2 != 0);
        return num1;
    }
}

面试题49：把字符串转成整数

public class Solution {
    public int StrToInt(String str) {
        if(str==null || str.length() == 0) return 0;
        char[] arr = str.toCharArray();
        boolean sign = true;
        int i=0;
        int res = 0;
        while(arr[i] == ' '){i++;}
        if(arr[i] == '+') {sign = true;i++;}
        else if(arr[i] == '-'){sign = false;i++;}
        for(;i<arr.length;i++){
            if(arr[i]<'0' || arr[i]>'9'){return 0;}
            int digit  = arr[i] - '0';
            if(sign == true && (Integer.MAX_VALUE - digit) / 10 < res){
                return Integer.MAX_VALUE;
            }else if(sign==false &&(Integer.MIN_VALUE + digit)/10>res){
                return Integer.MIN_VALUE;
            }
            res =res*10 + (sign==true ? digit:-digit);
        }
        return res;
    }
}

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