Leetcode notes: Perfect Squares

I. Title Description

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ... ) which sum to n .

For example, given n = 12 , return 3 because 12 = 4 + 4 + 4 ; given n = 13 , return 2 because 13 = 4 + 9 .

Two. Topic analysis

The main idea of this topic is to give a target integer that calculates the minimum number of the target integer by the total sum of squares.

A better solution is to use dynamic planning. We all know that a number x can be decomposed into an arbitrary number a plus a square number b * b , that is x = a + b * b . Therefore, the smallest number of squares that can form a target integer x is the a smallest number of squares plus 1 .

Three. Sample code

classSolution { Public:intNumsquares (intN) {Static  vector<int>Sqrtnum (1,0);if(Sqrtnum.size () >= n +1)returnSqrtnum[n]; while(Sqrtnum.size () <= n +1){inttemp = Int_max; for(intj =1; J * J <= Sqrtnum.size (); J + +) temp = min (temp, sqrtnum[sqrtnum.size ()-J * J] +1);        Sqrtnum.push_back (temp); }returnSqrtnum[n]; }};

Four. Summary

Another use of dynamic planning. Worthy of further study!

Leetcode notes: Perfect Squares