279. Perfect Squares ----M

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) {

vector<int> V;

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

V.emplace_back(i * i);

}

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

dp[0] = 0;

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

for (auto square : V) {

if (val - square >= 0) {

if (dp[val - square] != INT_MAX) {

dp[val] = min(dp[val], 1 + dp[val - square]);

}

}

}

}

return dp[n];

}

};