极值的问题一般考虑用DP
[LeetCode] Coin Change 硬币找零
http://www.cnblogs.com/grandyang/p/5138186.html
[LeetCode] Coin Change 2 硬币找零之二
http://www.cnblogs.com/grandyang/p/7669088.html
[LeetCode] Maximum Subarray(最大子串和问题)
http://blog.nlogn.cn/programming-pearls-the-maximum-sum-of-substring/
http://blog.youkuaiyun.com/liyuefeilong/article/details/49591517
http://blog.youkuaiyun.com/hhxin635612026/article/details/27373369