(java)Best Time to Buy and Sell Stock

Say you have an array for which the ith element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

思路:注意，本题只能进行一次买入和卖出的操作，本题可用贪心算法求解设置一个maxsun和一个low，当前的nums[i]比low小时，就把low变为nums[i]，这是贪心的典型特征，如果nums[i]-low>maxsum,就把nums[i]-low赋给maxsum，循环遍历这个数组就行了，注意本题的边界，就是数组中都是负的时候，找出那个最大的数就是了

代码如下(已通过leetcode)

public class Solution {
   public int maxSubArray(int[] nums) {
    boolean flag=true;
    int j=0;
    int temp=-Integer.MIN_VALUE;
    while(j<nums.length){
    if(nums[j]>0){
    flag=false;
    break;
    }
    if(nums[j]>temp) temp=nums[j];
    j++;
    }
    if(flag) return temp;
       int sum=0;
       int maxsum=0;
       for(int i=0;i<nums.length;i++){
        sum=sum+nums[i];
        if(sum>maxsum) maxsum=sum;
        if(sum<0) sum=0;
       }
       return maxsum;
   }
}