Lintcode: Minimum Subarray 解题报告

Minimum Subarray

原题链接： http://lintcode.com/zh-cn/problem/minimum-subarray/#

Given an array of integers, find the subarray with smallest sum.

Return the sum of the subarray.

注意

The subarray should contain at least one integer.

样例

For [1, -1, -2, 1], return -3

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SOLUTION 1：

1. 我们把整个array * -1，把它转化为求最大和的题目。

2. 然后我们可以使用Sliding window的方法来做。记录一个sum，如果发现sum<0 则丢弃，否则不断把当前的值累加到sum，

3. 每计算一次sum,求一次max.

4. 返回-max即可。

public class Solution {
    /**
     * @param nums: a list of integers
     * @return: A integer indicate the sum of minimum subarray
     */
    public int minSubArray(ArrayList<Integer> nums) {
        // write your code
        
        int len = nums.size();
        
        int max = Integer.MIN_VALUE;
        int sum = 0;
        for (int i = 0; i < len; i++) {
            if (sum < 0) {
                sum = -nums.get(i);
            } else {
                sum += -nums.get(i);
            }
            
            max = Math.max(max, sum);
        }
        
        return -max;
    }
}

GITHUB:

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/lintcode/array/SubarraySum.java