Why does int in my DP array cause overflow in Coin Change II problem?

Question

class Solution {
    public:
    int change(int amount, vector<int>& coins) {
        vector<unsigned int > dp(amount+1, 0);
        dp[0]=1;
        for (int value: coins){
            for (int i=value; i<amount+1; ++i){
                dp[i]+=dp[i-value];
            }
        }
        return dp[amount]; 
    }
};

this code works fine and runs on all the test cases

but .. this does not (only difference is the use of int instead of unsigned int)

class Solution {
    public:
    int change(int amount, vector<int>& coins) {
        vector<int > dp(amount+1, 0);
        dp[0]=1;
        for (int value: coins){
            for (int i=value; i<amount+1; ++i){
                dp[i]+=dp[i-value];
            }
        }
        return dp[amount]; 
    }
};

error- Line 8: Char 22: runtime error: signed integer overflow: 27131803 + 2123074792 cannot be represented in type 'value_type' (aka 'int') (solution.cpp) SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior prog_joined.cpp:17:22

After attempting to format them equally, the two samples appears to be identical. Is the format the only difference between the two? — Steven
– Steven, Commented Apr 15 at 6:52
As the error indicates there is an arithmetic overflow when using int instead of unsigned int. A 32-bit int has a maximum value of 2,147,483,647 while a 32-bit unsigned int has a maximum value of 4,294,967,295. en.cppreference.com/w/cpp/language/types — Jay Buckman
– Jay Buckman, Commented Apr 15 at 13:49
@JayBuckman that is not the problem as i have also used long long int, nut still it didn't work — OXEN
– OXEN, Commented Apr 15 at 16:13
Do you get the same error about "signed integer overflow", type 'int' when you use long long int? — Jay Buckman
– Jay Buckman, Commented Apr 15 at 18:50

Angus · Accepted Answer · 2025-07-07 01:41:44Z

0

To avoid overflow in addition operations, if all operands are positive integers and the ranges are known, during computation you can attempt to use uint32_t or uint64_t to prevent overflow

answered Jul 7 at 1:41

Angus

1

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