栈和队列_leetcode279-经典的层次遍历

#coding=utf-8
#点评：
#递归思想加层次遍历，很经典的解题模板思想  20181220



class Solution(object):
    def numSquares(self, n):
        """
        :type n: int
        :rtype: int
        """

        pair = (n,0)
        queue = []
        queue.append(pair)

        while queue:
            curPair = queue.pop(0)
            num = curPair[0]
            step = curPair[1]

            if num == 0:
                return step

            for i in range(1,num+1):
                if num - i *i >= 0:
                    nextPair = (num-i*i,step+1)
                    queue.append(nextPair)
                else:
                    break

class Solution2(object):
    def numSquares(self, n):
        """
        :type n: int
        :rtype: int
        """
        pair = (n, 0)
        queue = []
        queue.append(pair)

        #matrix = [[0 for i in range(3)] for i in range(3)]
        visit = [0 for i in range(n+1)]
        visit[n] = 1

        while queue:
            curPair = queue.pop(0)
            num = curPair[0]
            step = curPair[1]

            if num == 0:
                return step


            for i in range(1, num + 1):
                nextNum = num - i*i
                if nextNum >= 0:
                    if visit[nextNum] == 0:
                        nextPair = (nextNum, step + 1)
                        queue.append(nextPair)
                        visit[nextNum] = 1
                else:
                    break


class Solution3(object):
    def numSquares(self, n):
        """
        :type n: int
        :rtype: int
        """
        pair = (n, 0)
        queue = []
        queue.append(pair)

        #matrix = [[0 for i in range(3)] for i in range(3)]
        visit = [0 for i in range(n+1)]
        visit[n] = 1

        while queue:
            curPair = queue.pop(0)
            num = curPair[0]
            step = curPair[1]

            if num == 0:
                return step


            for i in range(1, num + 1):
                nextNum = num - i*i
                if nextNum >= 0:
                    if visit[nextNum] == 0:

                        if nextNum == 0:
                            return step+1

                        nextPair = (nextNum, step + 1)
                        queue.append(nextPair)
                        visit[nextNum] = 1
                else:
                    break



# 动态规划
class Solution4(object):
    def numSquares(self, n):

        return self.squareNum(n)

    def squareNum(self, n):

        self.memo = [n for i in range(n + 1)]

        self.memo[0] = 0
        self.memo[1] = 1

        # #memo[2]
        # for i in range(1, 2):
        #     if n - i ** 2 >= 0:
        #         self.memo[2] = min(self.memo[2],1+self.memo[n - i ** 2])
        #
        #
        # #memo[3]
        # for i in range(1, 3):
        #     if n - i ** 2 >= 0:
        #         self.memo[3] = min(self.memo[3],1+self.memo[n - i ** 2])



        for i in range(1,n+1):
            for j in range(1,i):
                if i - j ** 2 >= 0:
                    self.memo[i] = min(self.memo[i], 1 + self.memo[i - j ** 2])


        return self.memo[n]s = Solution2()print s.numSquares(13)