Leetcode Perfect Square---key _leetcode

https://leetcode.com/problems/perfect-squares/

Understanding:

Can have number theory, DP, BFS Three kinds of ideas to solve,

Number theory: recommended in this way

In this ref, it's a detailed story.

Http://www.cnblogs.com/grandyang/p/4800552.html

Solution II: Dynamic Programming (programming)

Time complexity: O (n * sqrt N)

Initialize the DP array to infinity; Dp[y * y] = 1, where: Y * y <= N. This means that the square is itself, so of course it turns out to be 1.

State transition equation:

Dp[x + y * y] = min (dp[x + y * y), dp[x] + 1)

Wherein: DP [i] represents the minimum number of squares and numbers required to gather into I, and x + y * y <= N

The transfer formula is dp[n] = 1 + min ([dp[n-j**2] for J-xrange (1, int (n**0.5) + 1)], which is the number of the current n corresponding Perfect square minus one, minus a perfect sq Uare, the rest must also have the least perfect square part, and the perfect square, which is to be subtracted, cannot be reduced arbitrarily, at most, minus its own sqrt

This version leetcode not allowed, timeout

Class Solution (object):
    def numsquares (self, N): ""
        : Type n:int
        : Rtype:int ""
        "
        if n<=0: Return 
            0
        
        DPS = [0]
        
        for i in xrange (1, n + 1):
            
            tmp = 1 + min ([dp[i-j * 2] for J-xrange (1, int (i**0.5 ) + 1)])
            dp.append (TMP) return
        Dp[-1]

But the mind is right.

Reference code: http://bookshadow.com/weblog/2015/09/09/leetcode-perfect-squares/

Http://traceformula.blogspot.hk/2015/09/perfect-squares-leetcode.html

BFS:

Extensive search:

Http://traceformula.blogspot.hk/2015/09/perfect-squares-leetcode.html