Find all the quadruples [a, b, c, d] where a^3 + b^3 = c^3 + d^3 when 1 <= a, b, c or d <= 10000 [closed]

Answer 1

One Solution - using concept of finding 2 sum in a sorted array. This is O(n3)

public static void pairSum() {
    int SZ = 100;
    long[] powArray = new long[SZ];
    for(int i = 0; i< SZ; i++){
        int v = i+1;
        powArray[i] = v*v*v;
    }
    int countPairs = 0;
    int N1 = 0, N2 = SZ-1, N3, N4;
    while(N2 > 0) {
        N1=0;
        while(N2-N1 > 2) {
            long ts = powArray[N1] + powArray[N2];
            N3 = N1+1; N4 = N2-1;
            while(N4 > N3) {
                if(powArray[N4]+powArray[N3] < ts) {
                    N3++;
                }else if(powArray[N4]+powArray[N3] > ts) {
                    N4--;
                }else{
                    //System.out.println((N1+1)+" "+(N2+1)+" "+(N3+1)+" "+(N4+1)+" CUBE "+ts);
                    countPairs++;
                    break;
                }
            }
            N1++;
        }
        N2--;
    }
    System.out.println("quadruplet pair count:"+countPairs);
}