279. Perfect Squares ----M

Q:

Given an integer n, return the least number of perfect square numbers that sum to n.

A perfect square is an integer that is the square of an integer; in other words, it is the product of some integer with itself. For example, 1, 4, 9, and 16 are perfect squares while 3 and 11 are not.

 

Example 1:

Input: n = 12
Output: 3
Explanation: 12 = 4 + 4 + 4.

Example 2:

Input: n = 13
Output: 2
Explanation: 13 = 4 + 9.

 

Constraints:

• 1 <= n <= 104

A:

明显就是个 DP 问题

class Solution {

public:

int numSquares(int n) {

int seed = 1;

vector<int> squares;

while(seed * seed <=n){

squares.push_back(seed * seed);

seed++;

}

// DP

vector<int> minSquare(n+1,INT_MAX);

minSquare[0] = 0;

for(int i =1;i<=n;i++){

for(const auto c : squares){

if( i - c >=0){

minSquare[i] = min(minSquare[i], minSquare[i-c] +1);

}

}

}

return minSquare[n];

}

};