#define STACK_SIZE 100000
#define Top_i (stack[sp-1].i)
#define Top_k (stack[sp-1].k)

struct STACK {int i; int k;} stack[STACK_SIZE];
int  sp = 0; /* stack pointer */

void push(int i, int k) {
    if(sp >= STACK_SIZE) {
        fprintf(stderr, "stack overflow\n");
        exit(2);}
    stack[sp].i = i;
    stack[sp++].k = k;
}

void pop() {sp--;}

void print_LDIs_stack(int N) {
    int j;
    push(0,0);
    for(j = 0; j < N; j++) {
        output(j, j, 0);
        while(lcp[j+1] < lcp[Top_k]) {
            output(Top_i, j, Top_k);
            pop();
        }
/* original code */
        push(Top_k, j+1);

/* efficient code */
/*
        if(lcp[Top_k] == lcp[j+1]) Top_k = j+1;
        else push(Top_k, j+1);
*/
    }
}